The conceptual profile of equilibrium and its contributions to the teaching of chemical equilibrium

Abstract

The learning of scientific concepts is one of the main research subjects in science education. Although little used, the theory of conceptual profiles allows the study of this knowledge, taking into account the presence of different ways of thinking about a certain concept in the same individual. This study aimed to build a conceptual profile for the concept of equilibrium and, based on this profile, relate it to the teaching and learning process of chemical equilibrium. Four zones were proposed to comprise the profile, called intuitive, static, kinetic and energetic. Subsequently, we analyzed the responses obtained in a questionnaire by students of Chemistry courses in order to group similar ways of speaking into categories related to the concept of equilibrium and the proposed zones for the conceptual profile. In the answers, we found some alternative conceptions already identified by the literature. Based on the results, the proposed zones for the conceptual profile of equilibrium indicate that establishing associations between the state of chemical equilibrium and the notion of equality can lead to conceptual errors and, therefore, it is suggested to give priority to the notion of stability. We also propose the use of studies on the History and Philosophy of Sciences applied to the teaching of chemical equilibrium to stimulate the emergence, dialogue and enrichment between the zones of conceptual profile in individuals.

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Introduction

The notion of equilibrium is one of the most comprehensive concepts that we use in our daily lives, even if unconsciously. A brief reflection on the variety of situations and possible uses of this concept evidences the richness of its application in several areas of knowledge, especially when considering the benefits that its study provides to society. As examples, we highlight the chemical equilibrium present in the following reactions, which stand out for their economic importance: (1) ammonia production (Haber–Bosch process); (2) production of nitric acid (Ostwald process); and (3) the dissolution of precious metals, e.g. gold and platinum, using aqua regia.

By centralizing our discussion in Science teaching, specifically in Chemistry teaching, we observe that one of the reasons why the concept of equilibrium in Chemistry is taken as a problematic issue is, according to Silva and Amaral (2017), the presence of a significant conceptual hierarchy regarding its understanding, since the concept of equilibrium is related to other concepts such as a chemical reaction, reversibility, entropy and free energy. The ability to relate these concepts is required to understand equilibrium in fundamental chemical reactions, such as those observed in biological and industrial processes (Silva and Amaral, 2017). Yan and Talanquer (2015) emphasize that understanding these concepts and theories may still not be enough, as students need to learn how to integrate them and know how to apply them properly in different contexts and situations.

Silva and Amaral (2017) also state that, due to the complexity of the concept and the degree of difficulty observed in some of the students, and even in some teachers, the teaching of equilibrium in Chemistry has been the subject of attention in research in chemical education. As a result, there are several studies in the literature dealing with the difficulties faced in teaching and learning chemical equilibrium (Machado and Aragão, 1996; Tyson et al., 1999; Locaylocay et al., 2005; Meneses, 2007; Carobin and Serrano, 2007). Locaylocay et al. (2005) state that problems frequently appear when students are introduced to the dynamic and reversible nature of chemical equilibrium, the Le Chatelier's Principle and the equilibrium constant.

Several obstacles have been associated with learning about chemical equilibrium. One of them is the lack of contextualization in its teaching, which can make the content uninteresting for those who are learning (Vasconcelos et al., 2016). The use of inappropriate analogies in an attempt to optimize students’ learning was also recognized as a source of difficulties by Raviolo and Garritz (2007). The emphasis on mathematical treatment for solving problems involving chemical equilibrium at the expense of deepening conceptual aspects is another difficulty for learning this concept (Júnior and Silva, 2009).

Research on learning scientific concepts was initially investigated using the conceptual change model (Posner et al., 1982). As a main premise, the authors argue that learners should abandon ways of thinking about a concept that are related to everyday life, that is, non-scientific ways of thinking, as these are considered obstacles to their correct learning. In this classical approach, conceptual change had to be achieved mainly through the creation of cognitive conflict (Duit et al., 2008).

This model was widely used by the scientific community and guided the proposition of didactic strategies for teaching Sciences in the last two decades of the last century. Subsequently, however, a limitation was observed in the application of the conceptual change theory in teaching practices, as it was found that students had difficulty letting go of their informal conceptions, which persisted even after several years of schooling. Considering the limitations of the conceptual change model, Mortimer (1995) introduced the notion of a conceptual profile, with which alternative ways of thinking are valued, including those related to their daily use, in view of the meanings that these ways acquire in different contexts. Lately, the notion of conceptual profile evolved through the incorporation of a sociocultural approach and pragmatist philosophy, becoming a theory of teaching and learning scientific concepts (Mortimer and El-Hani, 2014).

El-Hani et al. (2014) define three main objectives for the conceptual profile theory: to determine the zones that constitute the conceptual profiles for a number of concepts that are polysemic and have a central role in science education; to investigate how these zones appear in different subjects, as a way to characterize the individual conceptual profiles; to investigate the relationship between different ways of thinking and speaking in the classroom. Based on these objectives, we sought to contribute to this theory about teaching and learning that makes it possible to intervene in the dynamics of the classroom in an informed way and, therefore, according to El-Hani et al. (2014), it is first necessary to model the heterogeneity of speech and thought.

Considering that there is still no conceptual profile for equilibrium in the literature, and that its construction can help the proposition of didactic strategies for teaching chemical equilibrium, the objective of this study was: (1) to build a conceptual profile for the concept of equilibrium and; (2) to establish relationships among the proposed zones for the equilibrium profile and the teaching of chemical equilibrium.

This article is organized as follows: first, an overview of the main theoretical aspects that we consider important to reflect upon when reading the entire text; second, the details of the methodology used, as well as its advantages, disadvantages and limitations; third, the zones that construct the proposed conceptual profile for the concept of equilibrium; fourth, the analysis of the empirical data obtained by a questionnaire and discussions involving the proposed profile for equilibrium and its relationship with the teaching of this concept in Chemistry; and finally, our conclusions about the research.

Conceptual profile: theoretical aspects

Initially presented by Mortimer (1995), one of the foundations of the conceptual profile theory was the notion of epistemological profile proposed by Bachelard (1936/1978). There are similarities between the two types of profiles mentioned, since the different ways of thinking about a concept constitute different zones for the profile of an individual, in addition to the idea that the zones become more complex as the scientific content of the ways of thinking deepens. The Conceptual Profile theory, however, deviates from Bachelard's ideas, since it proposes that profiles can be integrated into a structure that considers the learning of concepts as the result of the acquisition of scientific language through discursive interactions in the classroom (Mortimer and El-Hani, 2014).

According to Mortimer et al. (2011), the conceptual profile theory has incorporated different notions of heterogeneity. One of these notions is based on Wertsch (1991), who proposed that the different ways of thinking can be classified according to their genesis. However, according to Wertsch, the most recently acquired ways of thinking are not considered more important than the previous ones. Another notion of heterogeneity was proposed by Tulviste (1991), who considered that a word can be polysemic in any culture and in any individual, both in scientific language and in everyday language. Thus, the construction of a conceptual profile seems to be important, since it allows a broader view of the concept and the different ways individuals understand it.

One of the ideas incorporated by the conceptual profile theory is Vygostsky's (1978) notion of conceptual thinking as one of the higher mental functions. Conceptual thinking is understood as an emergent process produced by the interaction between the individual and some external event or experience and, in this context, this process is always socially motivated. The stability of a meaning for a given concept is acquired through a recurring process, that is, when we are faced with a situation that we have already experienced, the same conceptual thinking already developed/acquired tends to emerge again. There is thus a process of internalizing/externalizing the assigned meanings directed to the cognitive system in a developmental relationship. Thanks to the dialectical character of this process, it is considered that an individual's ways of thinking and speaking can be conceived in the same way that they are in social languages: inherently interrelated (Mortimer et al., 2014a). For this reason, it is assumed in the conceptual profile theory that, for analysis purposes, they are equivalent.

The distinction between sense and meaning proposed by Vygotsky (1934/1987) was also incorporated. For Vygotsky, the sense of a word is the aggregate of all psychological facts that emerge from our consciousness as a reaction to that word, which can be dynamic and vary between different contexts. If a child has only one meaning for a word, that meaning may not coincide with the same meaning as that of an adult. Unlike sense, the meaning is stable and remains, even considering all forms of sense that are associated with the same word in different contexts. The ways of thinking should be treated as elements of permanence in the conceptual thinking of individuals (Mortimer et al., 2011), that is to say that they have a well-defined structure, as they are limited and converge in social interactions.

As Mortimer et al. (2012) state, concepts can be resumed in two ways: (1) as learners’ mental models or schemes of an object or event, which implies that concepts are relatively stable mental entities and are possessed by, or belong to, an individual; or (2) concepts and conceptualizations are distinguished and we can develop different ways of conceptualizing objects and events depending on the context. While the conceptual change theory approaches the former view, the conceptual profile approach is congruent with the latter.

Vygotsky (1934/1987) also assumes that socially available concepts and categories are similarly understood by individuals who share the same culture, so that this common understanding allows for effective communication between them. Based on these premises, according to the conceptual profile theory, each individual has their own profile for a given concept, and each profile is constituted by several ways of thinking which we call zones. Each of the zones also corresponds to a particular way of talking about this concept, and its structure is limited by sociocultural interactions. The variation between the individual profiles occurs in the weight of each zone which, in turn, will depend on the extent to which it is given the opportunity to be used profitably in the course of development to face the difficulties presented by our experiences.

For El-Hani et al. (2014), older ways of thinking are preserved and continue to function in appropriate contexts. That is why there is a consensus on the existence of two or more meanings for the same word, and this coexistence is possible even for scientific concepts, in which the dissonance between the classic and modern views for the same concept can exist. It should be noted, then, that different ways of speaking/thinking can emerge in the same sentence and that this is considered natural in the study of conceptual profiles. A part of the premises of the theory is the coexistence of different ways of thinking about the same individual – thus, heterogeneity is manifested at the individual level.

El-Hani et al. (2015) argue that, during conceptual learning, two processes are related: (1) the enrichment of an individual's conceptual profile, which means increasing the weight of each of their zones (cognitive process); and (2) making the individual aware of the multiplicity of ways of thinking that make up the profile, as well as the contexts in which they can be applied, according to their pragmatic value (metacognitive process). In the later, it is necessary to provide students with a clear view on how the ways of thinking can be differentiated from each other and, more than that, on which ways of thinking and speaking are appropriate for which contexts.

According to Mortimer and El-Hani (2014), only the concepts that follow these criteria should have their profiles built: (1) they must be central to science; (2) they must be polysemic enough for the building of their profile to be worthwhile; and (3) they must be present in both scientific and everyday language. We believe that the concept of equilibrium meets all these requirements. Once these criteria are met, three genetic domains must be studied, namely: sociocultural, ontogenetic and microgenetic. Therefore, we chose to follow the instructions described by Mortimer et al. (2014b).

In the construction of the sociocultural domain, secondary sources on the history of sciences are researched, as well as epistemological analyses of the concept in question. These analyses are particularly useful for understanding the attribution of meanings in this domain and for establishing ontological and epistemological commitments that will guide the process of signifying a concept. The sociocultural history of the concept will show what changes have occurred in the ways of thinking about it through the history of humanity, in addition to the impact caused by these changes.

One of the main instruments for the construction of the ontogenetic domain is the study of alternative conceptions about the chosen concept. It is investigated how the concept is learned and how it evolves in the history of each subject, making it possible to represent the processes of knowledge construction in everyday life. The possibility of finding these alternative concepts discussed in the literature in the empirical data raised for the proposition of the microgenetic domain should be considered, simultaneously encompassing two genetic domains, which can also reveal other conceptions, in addition to those previously identified.

Finally, the microgenetic domain consists of obtaining data collected through interviews, questionnaires and recordings of discursive interactions in a variety of contexts, especially educational ones, which provide access to the ontogenetic and microgenetic domains. The latter is linked to the microprocess or microgenesis that occurs in situations of interaction and involves the expression of ideas, frequently in a short time and in specific circumstances. To analyze this data, some researchers (Coutinho et al., 2005; Silva and Amaral, 2013) categorized the responses before proposing the zones, facilitating the constitution of the profile. Mortimer et al. (2011) highlight the need to further explore the subjects’ statements, in order to interpret them in terms of a repertoire of ontological and epistemological commitments elaborated as hypotheses, which are constantly reformulated by the researcher, in light of their data sources.

Methodology

According to Mortimer et al. (2014b), there are two ways to draw a profile. The first begins with the analysis of the data obtained in the construction of the microgenetic domain, performed in a partially inductive way, and the categories are constructed without taking into account the other two domains, that is, without the influence of the literature on the historical development of the concept and its epistemology, or the study of alternative conceptions. The risk, however, is to perform a very poor categorization of the empirical data, which increases the difficulty in interrelating these data with those from other sources. In addition, the analysis is not interrupted at this stage, since the proposed categories will probably not yet correspond to the areas of the intended conceptual profile. As the domains are identified by ontological and epistemological commitments, which are not commonly found on the surface of the discourse, a second stage is necessary, involving the construction of the other two domains to enrich the data obtained with the construction of the microgenetic domain.

The second type of strategy used to build the conceptual profile begins with historical/philosophical analysis and alternative conceptions as a method for choosing categories. This being done, the empirical data from interviews and questionnaires must be analyzed and categorized, taking into account this pre-arranged structure. Thus, the risk is to produce a very rich categorization with the first two domains and end up obtaining empirical data that is qualitatively insufficient to reach this high level of understanding. Another risk highlighted in the conceptual profile theory is the possibility of excessive bias in data interpretation. With that in mind, we chose to draw the conceptual profile of equilibrium using the second strategy.

Data for the study of the three conceptual domains, sociocultural, ontogenetic and microgenetic, were collected from their respective sources and, after analyzing all the material collected, it was possible to identify the ontological and epistemological commitments for the constitution of the profile zones. However, the intention is not only to establish parallels between the ways of thinking found in the domains, but to investigate the variety of thoughts attributed to the concept (El-Hani et al., 2014). During the course of the research, we used the Atlas.ti software, which made it possible to manipulate and organize the large amount of data collected, later transformed into codes and categories, which will be presented and discussed in the next section of this article.

Sociocultural domain

The historical evolution of the concepts of equilibrium and of the different ways of thinking/talking about them was surveyed. However, due to the wide range of applications of this concept in the most diverse fields of study, it was necessary to limit the domain based on notions of equilibrium only inserted in the context of Natural Sciences. We used the Cambridge's History of Science collection as the main source, allied to the various authors who, directly or indirectly, deal with the History and Philosophy of Science (HPS). Therefore, since it is not only a concept used in one area of knowledge, in addition to its use always being linked to one of these areas (e.g. chemical equilibrium), it was necessary to seek the semantics of the concept of equilibrium in dictionaries. We chose the dictionaries we consider the most important in Portuguese and English, as well as dictionaries specialized in natural sciences.

To make it easier to find the meanings, we will represent each one by a reference letter. The following were chosen in the Portuguese language: Dicionário Aurélio da Língua Portuguesa (A) (2019a); Grande dicionário Houaiss da Língua Portuguesa (H) (2019b); and Michaelis Dicionário Escolar da Língua Portuguesa (M) (2019c). Three were chosen in the English language: Cambridge English Dictionary (C) (2019a); Oxford Dictionary (O) (2019c) and Merriam-Webster (W) (2019b). At the same time, the history of the concept of chemical equilibrium and its epistemology was investigated to later relate them to the profile proposed for the concept of equilibrium.

Ontogenetic domain

It was not possible to obtain satisfactory results for the construction of the ontogenetic domain through the survey of alternative or informal conceptions within the Natural Sciences for the concept of equilibrium, since it is only used academically in an applied way in some branches of Sciences, but not in a generic way. However, we emphasize that, when studying the conceptual profile of equilibrium applied to any area, it is important to consider the study of alternative conceptions related to the specific concept. Chemistry was the only area in which we found studies on alternative conceptions for the concept, and this will be the focus of our discussions in a later section in this article.

Microgenetic domain

Finally, for the microgenetic domain, the guidelines found in Mortimer et al. (2011) were followed. Therefore, a questionnaire (Appendix A) was applied to 39 students of Chemistry courses (Major and Degree) at the State University of Southwest Bahia (UESB). The chosen group consisted of three types of respondents: (1) graduating students with a minimum of 80% of the curriculum of the course completed; (2) students recently graduated from the institution; and (3) master students of the Graduate Program in Chemistry at the same University. Most of the research found on chemical equilibrium involves high school students or undergraduate students in initial semesters, in addition to teachers, generally of basic education. For this reason, we decided to investigate a more academically advanced group, assuming that the content approach was presented to them in a more complex way, which could also increase the depth of the responses obtained.

Data collection and analysis

Data collection started in November 2017 and ended in March 2019. Once collected, the data were prepared for analysis using the Atlas.ti software. In order to obtain data regarding students’ ways of thinking/speaking about the concept of chemical equilibrium, the following questions were asked (Appendix A): Question 03 (Q03). “What do you understand by chemical equilibrium?”; and Question 04 (Q04). “How do you explain the origin of the chemical equilibrium state? In your answer, please describe the factors and conditions that you consider necessary for a reaction to reach that state.” Three of the answers were disregarded in Q03, since they did not make sense according to our proposal.

Data analysis was performed based on the ideas of cause and consequence, in which the answer to Q04 should be the cause for (Q03). In addition, we also investigated how students expressed the Le Chatelier's Principle in their answers to Q04. All responses were grouped into seven categories, which relate to the zones of the conceptual equilibrium profile previously proposed, as shown in Table 1.

Table 1 Relationship between the zones of the conceptual profile of equilibrium and the categories for the concept of chemical equilibrium

Equilibrium	Chemical equilibrium
Zones	Categories
Intuitive zone	Notion of equality
	Notion of stability
Static zone	Static state
Kinetic zone	Kinetic equilibrium
Energetic zone	Energetic equilibrium

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In this article, the data were obtained from several sources, thus collaborating to ensure its validity. The questionnaire was applied by the authors themselves and all data were reviewed several times. Data analysis was performed comparatively following the authors' perspectives. When any point of divergence was noticed, an attempt was made to establish a consensus in order to minimize any inconsistency found. It is important to mention that all data presented in this work were only collected after approval of the research by the institution's ethics committee (CAAE no. 76687317.3.0000.0055). In addition, all data were obtained in the local language (Portuguese) and then translated into English. The article has been translated by an experienced local English teacher and reviewed more than once by each of the authors. Unfortunately, even with all this caution, losses may have occurred due to the nature of the translation process.

The conceptual profile proposal for the concept of equilibrium

In this section, we will present the four zones proposed for the conceptual profile of equilibrium and the way in which they were constructed. Hence, we intend to highlight some historical events related to the concept, the meanings that were found in the dictionaries and the ways of thinking/speaking of the interviewees.

Intuitive zone

In this zone, we will discuss the way of thinking about equilibrium that is closely related to everyday experience. The word equilibrium derives from the Latin aequilibrium and means “equality of weight in the balance” (Nascentes, 1966). This source, however, does not indicate when this term started to be used.

Archimedes’ use of the term equilibrium is the oldest record we have found in the history of Science. The greek Archimedes of Syracuse (287–212 BC) wrote two main studies, De centris gravium (On the equilibrium of planes) and De insidentibus aquae (On floating bodies). The first study introduced mechanics based on pure mathematics and presented the determination of the center of gravity for several flat figures. In the same study, the author postulated that equal weights over equal distances are in equilibrium on a scale. In the second study, Archimedes brought to light his famous principle that is used to calculate the volume of objects in different ways after inserting them in fluids, among other contributions (Park and Daston, 2008).

The Oxford dictionary (2019), however, states that the term equilibrium originated in the early 17th century, in the sense of “a well-balanced state of mind”. We think that this way of thinking is also inspired by the use of scales, but we will not go further into this discussion, since this way of thinking is not inserted in the areas of knowledge of our research.

In the history of Science, Lavoisier started in 1789 a series of experiments through which he concluded that there were three types of regulatory processes for animals: respiration, digestion and transpiration, which should be in equilibrium with each other for the body to reach its material equilibrium (Nye, 2008). In Biology, the Hardy–Weiberg equilibrium considers that, in an idealized population of a given species, the frequency of the appearance of certain alleles that determine its characteristics will always be the same (Edwards, 2008). In this context, the number of individuals who have the same characteristic will maintain numerical equality, and thus equilibrium exists.

After surveying the semantics of the term equilibrium in the six used dictionaries, we observed that there are two patterns of definitions that make up this intuitive zone. The first encompasses meanings that indicate the sense of “quantitative equality” and was present in three dictionaries explicitly (A, H and M), while the other three left the sense of stability of a balance implicit. The second pattern consists of definitions that express the idea of physical stability of a body or constancy of a numerical value, and appeared only in A, H and M.

Some of the answers obtained in the application of the questionnaire that contained extracts attributed to the intuitive zone also involved the concept of force (this will be covered in the next subsection). The following answers only showed us the notion of equality:

Maintaining the equilibrium in a chemical reaction where the concentration of the reagents is equal to that of the products. (Q03R20)

Equal point, where the concentration of products and reagents remains constant. (Q03R30)

As there is no scientific deepening in the answers on how the equilibrium occurs, these answers are linked to the intuitive zone. By the notion of stability, however, it is understood that the concentration of reagents and products may or may not be the same and that is why it is necessary to be careful with the activities present in textbooks, which can confuse students. Here are some examples of this kind of answer:

Where there is a proportion of reagent and product it remains constant in the reaction. (Q03R04)

Chemical equilibrium occurs when both sides (reagents/products) have the same amount of matter (mass). (Q03R12)

The term equilibrium is related to “quantitative equality” and the notion of stability was also observed, either for the position of a body or for a numerical value, in which small oscillations may be noticed around a fixed number. The use of the word ‘proportional’ above suggests that the ratio does not necessarily have to be the same for each side, as long as there is stability between them. Seven other responses covered both notions. Therefore, the difference between these two notions is due to the presence of an alternative conception in the first one, namely that the concentration of the reagents is equal to that of the products in chemical equilibrium (Hackling and Garnett, 1985; Raviolo and Martínez, 2003; Carobin and Serrano, 2007) and, if it is equal, it does not vary, which is false according to chemical equilibrium theories.

When asked about the origin of chemical equilibrium, six students affirmed that the cause for the state of equilibrium was also the search for equality or stability between reagents/products and that it is directly linked to the intuitive zone of the equilibrium profile, as one can see below:

Substances tend to move to achieve a better state of stability, thus balancing a reaction. This requires an appropriate temperature, pressure and concentrations. (Q04R22, stability)

The equilibrium state occurs when the concentrations remain constant, for this reason, no external changes should occur, such as changes in temperature and pressure. (Q04R30, equality)

Static zone

In this zone are the ways of thinking about the concept of equilibrium related to the notions of “equality” and “stability” in the senses discussed in the intuitive zone. However, the static zone goes further, by incorporating scientific knowledge to those notions, a characteristic that differs from the previous zone. The idea from Physics about “forces that cancel each other out” is one of the most frequent, but its understanding, however, should not be limited to this notion, since the static state also leads us to think of a situation without movement or variation, it is not necessary to involve the concept of force to achieve equality between two or more sides. Therefore, we emphasize that the commitments pass from a material ontology (characterized by quantity and stability of something) to a procedural ontology, with which the individual seeks to explain the reason for obtaining equality or stability.

The strongest influence in this zone comes from Newton. His ideas were so very well-accepted by the scientific community that they seemed to inspire fields beyond mechanics. In his book Opticks (1704), he suggested that the bonds between chemical substances should be the result of the relationship between forces of attraction similar to gravitational forces. This idea is echoed in Boerhaave (1668–1738), who stated in his book Elementa chemiae (1724) that bodies exhibit forces of expansion and contraction inherent to the properties of matter, and maintain their volume while the temperature remains constant since the two forces are in equilibrium (Park and Daston, 2008).

Specifically in Chemistry, at the end of the 18th century, Berthollet was part of an expedition to Egypt led by Napoleon Bonaparte when he was intrigued to notice the continuous formation of sodium carbonate at the edge of a lake. He considered that there were a lot of reagents at the location, while the products of the reaction were constantly naturally removed. This observation contradicted the theory proposed by Bergman, according to which the formation of sodium carbonate would be impossible, since the reactions should be completed and present a unidirectional character (Quílez, 2009). When he returned from the expedition, Berthollet carried out several experiments and his results showed that the amount of substances present in the medium influenced the direction of the reaction. After confirming this idea through experiments, the reversibility of chemical reactions (one of the pillars of the concept of chemical equilibrium) was considered for the first time. He further stated that substitution reactions were never complete due to the equilibrium state between opposing affinity forces (Quílez, 2007). This is the first way of thinking about the concept of equilibrium in Chemistry, which was used in this case to mean the equilibrium between chemical forces, exactly the same terms used in mechanics (Lindauer, 1962).

In 1862, Berthelot and Saint-Giles considered that it was not appropriate to work with reactions between acids, bases and salts, which were the main subject of study on reversibility until then. Therefore, they began to intensively study chemical equilibrium in esterification reactions, especially since they were slower, and the quantities of each substance were always high enough to be measured (Quílez, 2006). Based on the study of Berthelot and Saint-Giles, Guldberg and Waage began to carry out various experiments that, after a few years, culminated in the proposition of the law of mass action. Based on Newtonian thinking, they assumed that chemical forces were not proportional to the amount of substances, but to their active mass (which we now know by concentration) (Quílez, 2018). It is highlighted that the terms previously introduced by Berthollet in Chemistry (“mass” and “sphere of action”) were important for Guldberg and Waage's understanding of chemical reactions. In addition, it must be remembered that they were not responsible for introducing the dynamic character in the concept of chemical equilibrium, since the Law of Mass Action was empirically developed, equalizing the two reaction directions (Quílez, 2018).

In the field of Geology, Clarence Dutton introduced the term “isostasy” in 1889, when he defended the idea that the earth was not an ideal sphere, with protuberances in which matter was lighter and depressions in which matter was heavier. Shortly after the beginning of the 20th century, John Joly, Frank Taylor and Alfred Weneger were the first who, separately, defended the idea of displacement of the continents. Initially, they were quite discredited until the large amount of evidence empirically obtained changed the understanding, which became that the huge masses of land moved since there was a fluid below them, causing them to float in hydrostatic equilibrium (Bowler and Pickstone, 2009). This movement was understood as a consequence of disturbances on the surface that soon ceased and, therefore, takes on a static character.

In 1972, Niles Eldredge and Stephen Jay Gould proposed a theory called “punctuated equilibrium” (Santos, 2013), where they argued that evolution is not a slow and continuous process, in which mutations are gradually shaped by the environment as Darwin originally thought, but stated that there were incremental and cumulative changes. According to them, what happens are punctuated evolutions caused by rapid changes in the environment, followed by periods of stasis in which stability dominates.

In the dictionaries, we found five meanings related to the static state of equilibrium. The predominance of the notion of “equality” between opposing forces is observed (A, H, M, O and W) over the notion of “stability” caused by opposite forces (A and H).

In addition, four responses evidenced thinking about the static character of equilibrium, and it was stated that products and reagents would no longer react with each other in a state of equilibrium, which is also one of the alternative concepts found in the literature (Hackling and Garnett, 1985; Raviolo and Martínez, 2003; Carobin and Serrano, 2007).

It is a chemical reaction in which the reagents are transformed into a product and the product can be transformed back into a reagent. It is a reaction that remains constant. (Q03R02)

Equilibrium is a chemical state where both the reagent and the product of a reaction are equivalent to each other and, therefore, stop reacting. (Q03R22)

About its origins, only one attributed a static character to reactions which are in equilibrium, bringing up the static zone, as shown:

The equilibrium state occurs when the chemical reaction is complete. It will normally depend on the environment, temperature and pressure of the reaction site and the concentration and physical state of the reagents. (Q04R34)

Kinetic zone

The first kinetic treatment of the concept of equilibrium appeared in 1850, when Williamson was conducting experiments to extend the carbon chain of a common alcohol at the time and obtained ethyl ether. Thus, not only did he elucidate the correct composition of water, alcohol and ether, but also developed a dynamic theory for chemical reactions. According to him, the reaction mechanism would be inconceivable if it were not thought of as a process of continuous exchanges between elements of a molecular aggregate (Quílez, 2006). Williamson concluded that a dynamic equilibrium would be the most plausible explanation for the experimentally obtained data, but he did not do any mathematical deepening with them. The results obtained by Wilhelmy in 1850 in his quantitative study of the sucrose inversion reaction also showed a dynamic character for chemical equilibrium. His study included mathematical calculations, but he did not attract the attention of the scientific community (Martorano et al., 2014).

The next scientist to propose a dynamic character for equilibrium was Maxwell (1867), who defined that, at equilibrium, the collision rate of the molecules of the direct reaction would appear at a given final speed equal to the collision rate that carried out the inverse transformation. His theory also assumed the existence of an equilibrium in which the number of molecules that moved in a given speed range would be uniform over time (Nye, 2008). Also in 1867, Pfaundler wrote an article in which he approached chemical reactions from the point of view of the kinetic theory developed by Clausius for evaporation and condensation of liquids in closed systems (Quílez, 2006), being the first to apply the mechanical theory of heat for chemical reactions. For Pfaundler, molecules would collide with each other to react, but not all collisions would be effective, and only molecules with sufficient kinetic energy could dissociate and recombine through collisions (Quílez, 2017a).

In biology, H. C. Cowles studied the vegetation of the Lake Michigan coast in 1901 when he came to the conclusion that plant societies should be constantly succeeding in the landscape, considering the very shifting topographic forms of the dunes present there. In his view, one plant society would necessarily need to be supplanted by the other over time, forming a dynamic equilibrium process. In this case, we would be dealing with the rate of appearance and disappearance of plants over time, showing that their speed must be equal or stable (Bowler and Pickstone, 2009).

For this zone, only the dictionaries C, O and W exposed the dynamic character of equilibrium relating it to kinetics, and we emphasize that they are all in the English language. In addition, we found a predominance of the kinetic character in almost half of the answers (17 of them) for Q03, as shown below:

Chemical equilibrium is the condition in which the concentration of a species does not vary liquidly over time. This is because the same amount consumed of this species is formed, almost instantly. (Q03R10)

Chemical equilibrium refers to reaction systems, where the rate of formation of products is equal to the rate of formation of reagents. (Q03R13)

These students stated that, in order to reach the equilibrium state, the speeds of the direct and inverse reactions should be equal. Also, 16 answers related to kinetic equilibrium were obtained for Q04. Two examples can be seen below:

The state of chemical equilibrium occurs from the equalization of forward and reverse speeds in a reversible reaction. As product species are formed, they react by re-forming the species of the reagents; when the speeds of these two reactions equal, equilibrium is reached. This may vary according to the reaction conditions such as temperature and pressure, as well as factors such as the concentration of reagents. (Q04R03)

The chemical equilibrium arises as the reagent is consumed and product is formed, there is also a product becoming a reagent, in this case the time will come when the speed at which the product is formed is equal to the speed at which the product is transformed into a reagent, there we have the chemical equilibrium. (Q04R33)

Again, this was the highest number among the categories, and consequently, also between the zones. This number is quite high, considering that the objective of the question was to seek information about the possible causes for the state of equilibrium.

Energetic zone

This zone is the one of which we find the least records in the history of science, and most of them are inserted in Chemistry. Its first mention appears in 1884, when J. G. van't Hoff published Studies in Chemical Dynamics, presenting considerations about the dynamic nature of chemical equilibrium, including the representation of the double arrow to replace the equal sign (Quílez, 2017b). He described the variation of the equilibrium constant as a function of temperature, in addition to developing the same Law of Mass Action proposed by Guldberg and Waage in a different way and entirely based on thermodynamic calculations.

When chemical kinetics and thermodynamics consolidated, van’t Hoff advanced his studies on the Law of Mass Action, saying that the maximum work done by a chemical process could be taken as a measure of the chemical affinity in the reaction. In addition, he indicated that the Law of Mass Action was valid only for isothermal systems, and that the influence of temperature on equilibrium could be determined through considerations involving the second law of thermodynamics, proposed by Clausius in 1850 (Lindauer, 1962).

The term ‘disgregation’ (lately, dissociation) was also a term introduced by Clausius as a measure of the separation of parts of a system from one another. The explanation of this phenomenon had been accounted for by Pfaundler using kinetic assumptions, but Horstmann also gave his explanation using, not a kinetic theory, but the second law of thermodynamics. The issue was the observation that, for some compounds in the gaseous phase, it appeared that the number of molecules present in the gas was not constant. Hortsmann's explanation for those deviations led to the first successful application of the thermodynamic concept of entropy to chemical reactions. Looking for the empirical meaning of Clausius's entropy, Horstmann found that in dissociation processes the equilibrium state is reached if the entropy of the system is at a maximum (Quílez, 2009).

Josiah Willard Gibbs, in the 1870's, argued that in any spontaneous chemical reaction, entropy (a measure of the unavailability of energy) must increase. Gibbs demonstrated that, in any chemical reaction at a given temperature, there is a simple relationship between the variation in enthalpy (amount of energy that must be absorbed or released in the reaction) and entropy, thus establishing a third quantity called the chemical potential (Verzoto, 2008).

In 1884, van’t Hoff further formulated the principle of mobile equilibrium, which was later simplified by Le Chatelier and ended up being popularized by the name of the latter (Lindauer, 1962).

Seeking more accurate calculations, Gilbert Newton Lewis, in 1907, introduced the concept of fugacity, a thermodynamic quantity measured in pressure units, which is related to the chemical potential of a substance. This concept expresses the ability of a given substance to escape from one phase to another (Verzoto, 2008). For Lewis, the system reached the equilibrium condition when the fugacity of a substance was constant. In 1923, Lewis also replaced the term chemical potential with free energy in honor of Gibbs (ΔG) (Verzoto, 2008).

In Biology, Arthur Tansley stated at the beginning of the 18th century that, in an ecosystem, the components are in a stable dynamic equilibrium (Bowler and Pickstone, 2009). This idea was expanded in 1944, when Erwin Schrodinger interpreted living beings from a thermodynamic point of view. For Schrodinger, living beings could delay their death, that is, the moment when they reach the maximum possible entropy, through metabolic processes. The brothers Eugene and Howard Odum, Tansley's students, followed their professor's model of thinking, understanding an ecosystem as a thermodynamic machine capable of maintaining itself in a state of oscillating equilibrium around its climax (Bowler and Pickstone, 2009).

For this zone, no meaning was found in the researched dictionaries that related to the concept of equilibrium with that of energy. Unfortunately, only one answer covered a concept of thermodynamics for this question, although without going further into it, as one can see:

In short, it is the process of maintaining the formation of reagents and products at the same speed, reaching an appropriate chemical potential. (Q03R36)

For Q04, the chemical equilibrium was justified based only on the energetic notion in one response:

Like any chemical reaction, chemical equilibrium is the search for the lowest energy level, for an ideal rearrangement of molecules, reaching the lowest energy level. (Q04R05)

Relationships between the conceptual profile of equilibrium and the teaching of chemical equilibrium

When we related the results of the questionnaire to the proposed zones for the conceptual profile of equilibrium, we noticed that the intuitive zone was still very present in the students’ writing. Regarding this zone, we suggest that the notion of equilibrium is strongly linked to the functioning of the balance and that it guides the initial thinking about this concept. Despite presenting a language close to that of science (e.g. products, reagents), the students’ answers distance themselves from the scientifically agreed conceptual elaboration. As a result of our analysis, it was possible to perceive the association between the concept of equilibrium related to notions of equality or stability, changing only how the students understood their origin. The concept of equilibrium is still heavily influenced by the original meaning related to the use of balance, and our study highlights these implications between balance and equilibrium.

One of the things that caught our attention was the use of the term “net variation” by two respondents, in reference to the amount of reagents and products, in the same way that it is used in financial mathematics to express cash flow, in which input values and outgoing money are calculated. For these respondents, the quantities of reagents and products would remain stable, even with the continuation of the chemical reaction.

We understand stability as the state of something that does not undergo changes, or, if it does, that these changes do not deviate from a predicted average. Moreover, being stable does not mean being dynamic (when variations happen at certain intervals of time, but are not interrupted). An alternative is to use the words “proportion” and “constant” in the intended sense, taking into account the stoichiometry between products and reagents (Locaylocay et al., 2005).

It is clear then that, for some respondents, the reaction does not need to be dynamic for reversibility to exist, evidencing the alternative conception that, in the state of equilibrium, the effect of concentrations is understood as a pendular behavior. That is, the reaction would only happen when any system variable changed, either for the formation of products or reagents, and would return to equilibrium soon after, in other words, stopping until another external influence appears. By conceiving the equilibrium state as two opposing forces that cancel each other out even after a variation, we consider that the static state category is the basis of the static zone. Considering that some of the respondents are, at least, about to conclude their graduation, the presence of these conceptions is cause for concern. They indicate that, during the course, difficulties in understanding the concept seem not to have been identified.

Some responses did not necessarily contribute to generating a conceptual profile zone:

Chemical equilibrium is demonstrated by the reaction in which certain conditions tend to form products or return to reactants. Dependent on physical conditions (such as temperature or pressure) and chemical (amount of reagent added). (Q03R07)

Equilibrium comes from the reversible process of a reaction. This state of equilibrium is based on the Le Chatelier's Principle where the variables: temperature, pressure, concentration can displace or favor the formation of some chemical reaction compound. (Q04R17)

This is the case of responses referring only to the system variables, which, despite highlighting the reversibility of reactions, did not provide more information on how equilibrium could be achieved. We also noticed that most students have already left the state of equilibrium to return to it even after a disturbance, and this makes us think about what position they would have if it was specified that the reaction would initially only take place with the presence of reagents in the medium. That leads us to think that this conception needs to be explored in other research, since new questions should be asked to deepen the students’ understanding of this point of view. Despite having some scientific basis, they did not provide us with any information about what the conditions were for the equilibrium to occur, and therefore it was disconnected from the proposed zones. Also, four responses limited the occurrence of the state of equilibrium to reactions that occur in a closed system, an alternative conception that appears in the review study conducted by Raviolo and Martínez (2003).

It is important to note that stability associated with speed of reactions characterizes the equilibrium kinetic zone. Since most of the students expressed themselves in a similar way, we can say that the kinetic zone predominates over the respondents' way of speaking and thinking. This idea is further from spontaneous thinking; therefore, it presents a conceptual elaboration derived from formalized teaching, and is more correct from a scientific point of view.

From a kinetic point of view, it is possible to obtain information on how reactions occur from their initial condition till the equilibrium state, or on how the equilibrium is reached after some disturbance caused by external factors. In addition, it is possible to determine the amount of substances present in the system over time, as well as to predict how the system's variables can alternate the equilibrium state (Le Chatelier's Principle). In short, equilibrium is a dynamic state in which the products are formed in the same rate that the reagents are consumed. In other words, when the direct and inverse reactions occur simultaneously with the same speed.

We thus reinforce that the equality of speeds is a consequence, and does not cause the state of equilibrium, that is, when stating that the reaction is in equilibrium since the speeds are equal, the reason or cause for reaching this point is not explained, and this is when thermodynamics should, in our opinion, be used.

In addition, there appears to be a relationship between the kinetic character for chemical equilibrium and the intuitive zone. Perhaps the respondents associate equality between two sides (intuitive zone) with equality between quantities of mass or concentration of reagents and products in a reaction, and also with equal speeds for the formation of both (kinetic zone), making the unconscious use of this relationship between equalities a factor that compromises the conceptual learning of individuals. This could also explain, albeit partially, the students’ difficulties in acquiring this concept from the perspective of thermodynamics.

When questioning the origin of the equilibrium state, we expected that the responses involved thermodynamic causes, given its fundamental character for the understanding of a reaction system, but we obtained a very small number of responses associated with that zone. Nevertheless, the absence of thermodynamic concepts (e.g., potential energy, entropy, free energy) in the respondents’ data suggests little familiarity with the concepts related to the energetic zone (and, in turn, with thermodynamics itself), and leads us to reflect on the contribution of this content to conceptual learning about chemical equilibrium. This answer that follows was the only one that presented all the correct ways of thinking chemically for the concept of chemical equilibrium:

Chemical equilibrium is caused by the thermodynamic factors of the reaction. In theory, all chemical reactions are reversible to some extent. However, for some, the equilibrium condition is almost completely shifted in one of the directions. From the thermodynamic point of view, the state of equilibrium occurs due to the tendency of the system to reach a condition of less free energy or chemical potential (μ). As the value of the chemical potential approaches zero, the speeds of the forward and reverse reactions become closer and closer. Another factor on which chemical equilibrium is dependent is temperature since, as the value of T changes, as well as in the case of free energy, the value of the equilibrium constant also changes. Thus, changing one of these variables has implications for the value of the relationship between products and reagents and, consequently, for the extent of the reaction. (Q04R10)

For Sabadini and Bianchi (2007), for example, the approach to the concept of chemical equilibrium should be preferable based on the point of view of thermodynamics, including discussions on the speed of reactions for chemical kinetics. For these authors, textbooks that approach the concept of chemical equilibrium from the point of view of chemical kinetics, fail to present readers with the fact that chemical reactions are governed by universal laws that describe the transformations of nature.

From a thermodynamic point of view, we can establish that chemical equilibrium is a state of maximum stability towards which a chemical system spontaneously tends, at fixed temperature and pressure. Thermodynamics demonstrates that the variation of the Gibbs free energy (ΔG) is the quantitative key that tells us the sense of stability for a physical or chemical transformation. From this point of view, it is possible to determine the conditions of temperature and pressure that favor the formation of a particular product, knowledge that has a high impact on the chemical industry.

Implications of conceptual profile theory for learning scientific concepts

Becoming aware of a conceptual profile and the demarcation between its zones implies being able to apply a scientific idea in the contexts in which it is appropriate and, at the same time, preserve ways of thinking and speaking different from the scientific in situations in which these modes prove to be pragmatically appropriate (Mortimer et al., 2011). This is particularly important when we think about teaching chemistry, as a student hardly understands this multiplicity of meanings as a natural characteristic of science (Mortimer and Amaral, 2014). If the students made little use of the thermodynamic way of thinking, we can understand, according to the conceptual profile theory, that the amount of experiences they had was not enough to cause a permanent deepening in the zone, culminating in its weakening. This can occur both as a consequence of the teacher's approach method and the lack of the student's engagement. It is important to consider, of course, that students may be in a cognitive development process in which they have mastered an idea, but are not yet aware of how to fit it into the heterogeneity of their own thinking (Mortimer and El-Hani, 2014).

Meneses (2007) states that some of the difficulties for learning the concept of chemical equilibrium come from the application of algorithms to the detriment of the conceptual explanation in textbooks and also from the decontextualization of the content, which is presented in a disconnected way from the students’ daily lives. Good analogies can help students acquire an abstract concept, as in the case of chemical equilibrium. Silva and Amaral (2015), for example, discuss the analogy that relates the concept of chemical equilibrium with the liquid/vapor water equilibrium. This type of analogy uses a physical change as analogous to a chemical reaction, but is limited to helping explain its dynamic character.

In addition, some conceptual errors can occur, as seen during the analysis of the answers to the sixth question of our questionnaire: “Describe chemical equilibrium situations that can be observed in our daily lives”. We obtained seven responses in which this confusion between chemical and physical changes was present. Additionally, in one of the dictionaries (O), there is also this erroneous meaning from the chemical point of view: “Chemistry. A state in which a process and its reverse are occurring at equal rates so that no general change is taking place. ‘Ice is in equilibrium with water’” (our translation). That is why it is necessary for the teacher to show to students what the similarities and differences are between the two types of changes that happen in the two systems, differentiating physical from chemical changes. Otherwise, students may not understand that, for an equilibrium to be considered chemical, there must be a chemical reaction, while the analogy involves only a change of physical state for the same substance. Therefore, if the analogy is not discussed considering its possibilities and limitations, it can lead the student to become more confused or even to construct misconceptions.

Theories of conceptual development tend to take this process as an effort towards a non-contradictory and uniquely correct path of conceptualization, which can supposedly subsume all other forms of conceptualization considered to be “inferior” (Mortimer and El-Hani, 2014). On the other hand, a theory that assumes the multiplicity of meanings and ways of speaking as a basic premise places the apprentice of science in a much more coherent place, according to their condition of belonging to different communities and that implies dealing with different points of view.

In order to alleviate the difficulties encountered in teaching the concept, some strategies were listed by Silva and Amaral (2017) and involve experimentation (Maia et al., 2005), the use of analogies (Raviolo and Garritz, 2008) and educational games (Soares, 2013). Silva and Amaral (2017) also proposed that the articulation of the levels of representation and understanding of chemical knowledge described by Johnstone (2000) could be used.

For Quílez (2004), defender of the History and Philosophy of Science (HPS) approach to teaching chemical equilibrium, the historical reconstruction of the concept of chemical affinity allows teachers to challenge students’ first ideas about chemical reactions, such as that the processes are carried out in only one direction and continue until one of the reagents is completely consumed. The author also states that teachers can use the history of the concept of chemical equilibrium to promote conceptual change in students. But the pragmatic value of everyday language will preserve meanings that are at variance with scientific understanding (Mortimer and El-Hani, 2014) and that is why we argue that one should not seek conceptual change in an individual, but rather make them capable of viewing the multiplicity of ways of thinking that can exist for the same concept. This way, students do not have to abandon alternative and unscientific ways of thinking about the concept, but rather recognize them as inconsistent with current scientific knowledge.

Therefore, it is possible to introduce the conceptual profile theory and encourage students to seek a better way of thinking for the context in question (Mortimer and El-Hani, 2014). With this objective in mind, the focus of the conceptual profile theory has turned to its applications in the classroom in the last few years. We highlight some recently published articles that used the theory to elaborate teaching and learning sequences (Guimarães et al., 2019; Oliveira and Piuzana, 2020; Sepulveda, 2020) and analyzed the patterns of discursive interactions in the classroom (Silva and Amaral, 2017).

Specifically, regarding chemical equilibrium, we suggest as the possibility to explore and discuss the kinetic and energy zones in the classroom the effects of pressure variation in a reaction system using the kinetic and energetic zones of the conceptual equilibrium profile. One can use, for example, some reaction between gases, as long as their enthalpy is less than zero (ΔH < 0), such as the Haber–Bosh reaction:

N_2(g) + 3H_2(g) ⇌ 2NH_3(g) ΔH = −92, 22 kJ

From the point of view of the kinetic zone, the increase in pressure will cause the total volume of the gases to decrease, favoring an increase in the speed of formation of the product (NH₃) to compensate for this disturbance (Le Chatelier's Principle). This could also be explained by the increase in the number of effective collisions between the reactant molecules (collision theory) since they are stoichiometrically more numerous and will be in a reduced space, causing them to collide more often.

It can also be stated that the work exerted on the mixture of gases will increase the amount of energy in the system, causing the entropy to increase as well:

ΔS = ΔQ/T

Since the reaction is exothermic and the entropy value will be positive, the Gibbs Energy for the reaction will be negative:

ΔG = ΔH − TΔS

In this case, the result would be the spontaneous favoring of the formation of products until a new equilibrium is reached.

This article does not contemplate the third objective of the theory of conceptual profiles mentioned by El-Hani et al. (2014), which is to investigate the relationship between different ways of thinking and speaking inside classrooms. This study will be conducted separately due to its extension and complexity, and for these reasons we must make it clear that the potential situations where the notion of conceptual equilibrium profile in chemistry appears need to be further discussed.

Conclusions

This study had as its main objective the construction of a conceptual profile for equilibrium, as a subsidy for the teaching of chemical equilibrium. We proposed four zones for this profile: intuitive, static, kinetic and energetic. We suggested that the different areas of Natural Sciences will present these zones in their particular conceptions of equilibrium in some way, enabling the use of theory in the evaluation of an individual's conceptual evolution, while simultaneously verifying the existence of alternative conceptions in their thinking.

Considering that the final goal is the emergence or enrichment of the profile zones, we recommend the use of the notion of stability rather than the use of the notion of equality for teaching chemical equilibrium. Due to its strong link with the sense related to the scale and, consequently, with the intuitive zone, the notion of equality requires that teachers be prepared to limit their sense when applied to the teaching of chemical equilibrium. As a suggestion, we indicate the use of the words “proportions” and “constants”, instead of the term “equal” when referring to concentrations.

Despite their academic level, some respondents still showed in their responses the way of thinking related to the static equilibrium zone for chemical equilibrium. This reinforces the importance of the conceptual profile theory, to reveal the different possible understandings for the concept and, although this way of thinking does not align with the scientific view (even if it was present in the historical development of the concept), it is important so that its limitations can be highlighted in the learning process.

When relating the profile zones with the chemical equilibrium categories, it was evident that none of the students related the kinetic character to the broader concept of equilibrium, in contrast to their responses to chemical equilibrium, as most defined it as the result of equal formation rates between products and reagents. Starting from the assumption that the notion of equality has a great weight in this way of thinking, it is possible to associate the equality present in the concept of equilibrium with the equality of the direct and inverse reactions in a chemical equilibrium. For us, students internalize the kinetic character more easily, due to this equality relationship.

Among the possible obstacles to learning and enriching the energetic zone, the relationship between equalities explained above may be one of them. Kinetics is understood by most respondents as the origin of the state of equilibrium when, in fact, it is a consequence. Very few of them conceived the real cause of the state of equilibrium with the search for stability in the reaction medium with thermodynamic factors. It can be assumed, based on the conceptual profile theory, that the absence of thermodynamic concepts in the responses is due to the small number of situations and experiences in which these respondents used these concepts in solving problems.

We reinforce that the conceptual profile proposed in this study can be improved. Our proposition lacks research that analyses data on the third objective of the theory, which is to investigate the appearance of zones in the classroom discourse. We highlight the use of History and Philosophy of Sciences as a strategy to be implemented in the classroom, since there are already well-founded studies in these areas, with results available in the literature and which, if adapted, would be able to cover all the zones proposed for the profile.

Conflicts of interest

There are no conflicts to declare.

Appendix A: questionnaire for surveying knowledge about equilibrium

Graduating student ( )/Graduate ( )/Master student ( )

Please answer the following questions:

(1) What do you understand by equilibrium?

(2) What types of equilibrium do you know?

(3) What do you understand by chemical equilibrium?

(4) How do you explain the origin of the chemical equilibrium state? In your answer, please describe the factors and conditions that you consider necessary for a reaction to reach that state.

(5) With which keywords would you describe the concept of chemical equilibrium?

(6) Describe chemical equilibrium situations that can be observed in our daily lives.

(7) What areas of Chemistry do you relate to chemical equilibrium?

(8) Consider the following problem situation:

Ozone (O₃) is a gas found in the atmosphere, mainly in the stratosphere. At low altitudes, it reacts with other compounds causing the effect of acid rain, harmful to the environment. At high altitudes, it forms the protective layer located around our globe, whose function is to filter UV-B solar rays. Excessive exposure to these rays can cause serious problems, such as damage to vision, premature aging, suppression of the immune system and skin cancer. Explain how the ozone layer maintenance process chemically occurs.

Acknowledgements

The authors would like to thank CAPES for the financial support.

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