Using think-aloud protocols to investigate secondary school chemistry teachers’ misconceptions about chemical equilibrium

Abstract

Secondary school chemistry teachers’ understanding of chemical equilibrium was investigated through interviews using the think-aloud technique. The interviews were conducted with twelve volunteer chemistry teachers in Hong Kong. Their teaching experience ranged from 3 to 18 years. They were asked to predict what would happen to the equilibrium system N₂(g) + 3H₂(g) ⇌ 2NH₃(g) if a small amount of nitrogen gas is added to the system at constant pressure and temperature. Analyses of the transcribed protocols indicated that regardless of the teachers’ years of teaching experience, none of the twelve teachers were able to solve the chemical equilibrium problem. An over-emphasis of Le Châtelier’s principle was found to be a major contributing factor to teachers’ problem-solving failures. They held the misconception that one can always cause an equilibrium system to shift to the right by increasing the concentration of a reactant. The interviewed teachers were classified into two problem-solving categories based on their cognitive sources of failures. Excerpts from the transcripts discuss the differences between the two categories as well as the hints given to teachers to help them solve the chemical equilibrium problem.