CHEMISTRY · Single correct · AP · Chemistry · Thermodynamics and Electrochemistry · Thermodynamics and Electrochemistry
Problem
Compound A can rearrange to form isomers B and C. At 20 °C the mixture is allowed to react for 1 min and is found to contain 90 % B and 10 % C. After the same mixture is heated at 80 °C for several hours, the composition changes to 10 % B and 90 % C. Which statement best explains this observation?
(a) The pathway leading to C has the lower activation energy, and increasing the temperature shifts the equilibrium toward C according to Le Châtelier’s principle.
(b) B is the more stable isomer (lower ΔG), but at 80 ∘C the faster reaction pathway to C dominates, so C prevails.
(c) The pathway leading to B has the lower activation energy, whereas C is more stable (lower ΔG); higher temperature and longer time allow the system to favor C.
(d) The increase in temperature causes the TΔS term to dominate, making the formation of C spontaneous; therefore B is converted to C as temperature rises.