In an industrial process, ethyl ethanoate (ethyl acetate), CH₃COOC₂H₅, is manufactured via the esterification of acetic acid (ethanoic acid) with ethanol:

CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O  ΔH = –4.9 kJ/mol

This equilibrium is mildly exothermic. The reaction is typically conducted in large batch reactors at 60 °C. A catalyst such as concentrated sulfuric acid is used to increase the reaction rate but does not alter the position of equilibrium.

Operators are advised that although increasing temperature can improve the rate of reaction, it may compromise product yield due to thermodynamic considerations. To optimise conversion, excess ethanol is used, and the water product is distilled off during the process, shifting the equilibrium toward ester formation.

In a pilot plant trial, technicians accidentally increased the operating temperature from 60 °C to 85 °C. Although the rate of formation increased, the final amount of ethyl ethanoate collected at equilibrium decreased. A subsequent trial involved the same temperature increase, but this time they also continuously removed both water and ethyl ethanoate as the reaction proceeded. The result was a significant increase in overall conversion compared to the baseline conditions at 60 °C.

Question 1

In the absence of any removal or addition of reactants or products, increasing the temperature of this system is most likely to:

A. Increase the equilibrium constant and shift the equilibrium toward ester formation.

B. Decrease the equilibrium constant and favour the reverse reaction.

C. Leave the equilibrium position unchanged, as the enthalpy change is small.

D. Increase both the rate and yield of ethyl ethanoate due to higher kinetic energy.

Question 2

The primary reason the second trial (85 °C with simultaneous removal of water and ester) resulted in greater conversion is that:

A. Le Chatelier’s principle predicts that removing products favours the forward reaction.

B. The rate of backward hydrolysis of ethyl ethanoate is lower at higher temperatures.

C. The catalyst is more effective at higher temperatures when water is removed.