Ethane can be formed by reacting acetylene with hydrogen. C₂H₂(g) + 2H₂(g) ⇄ C₂H₆(g) ΔH°_rxn = −311 kJ
Under which reaction conditions would you expect to have the greatest equilibrium yield of ethane?

Question

Quizplus · Accepted Answer

According to Le Chatelier's principle, increasing pressure shifts the equilibrium towards the side with fewer moles of gas. In this reaction, the reactants have three moles of gas (one for acetylene and two for hydrogen) while the product, ethane, has only one mole of gas. Therefore, higher pressure would favor the reactants and lower pressure would favor the products. Additionally, the forward reaction is exothermic (ΔH°_rxn = −311 kJ), meaning it releases heat when it proceeds in the forward direction. According to Le Chatelier's principle, increasing temperature shifts the equilibrium in the direction that absorbs heat. Therefore, lower temperature would favor the product formation in this exothermic reaction. Thus, the best conditions for the greatest equilibrium yield of ethane are low temperature and high pressure, which corresponds to option B.

Ethane Can Be Formed by Reacting Acetylene with Hydrogen