Chemical equilibria. Part 2.—Dehydrogenation of propanol and butanol
Equilibrium constants for the systems containing propanol + propanal, and butanol + butanal were derived from measurements of the composition of mixtures obtained when the vapours were passed with hydrogen over a catalyst held at a measured temperature. Equations expressing the changes in Gibbs energy, enthalpy and entropy of the reactions over a range of temperature were calculated from the measurements, with the aid of heat capacity data. By coupling thermodynamic data for the reactions with thermodynamic data for the appropriate alcohol, the standard heats of formation of liquid propanal and butanal were calculated to be –52.64 and –56.90 kcal mole –1 respectively, and the standard entropies of liquid propanal and butanal were calculated to be 48.2 and 59.4 cal deg–1. mole–1 respectively. The above values for the heats of formation agree with values derived from heat-of-combustion measurements; the value for propanal indicates an unusual thermochemical stability in this compound. The value derived for the standard entropy of butanal agrees with a published value obtained by low-temperature calorimetry, but the value derived for the entropy of propanal (ideal gas) does not agree with a published value obtained by statistical mechanics.