Which of the following best defines a coupled reaction in chemical thermodynamics?
a) Two reactions are considered coupled when their ΔH∘ values sum to zero, so the overall enthalpy change is neutral even if ΔG∘ is not.
b) A reaction is said to be coupled when the addition of a catalyst makes it spontaneous despite no change in ΔG∘.
c) An unfavorable reaction proceeds by sharing a common intermediate with a highly exergonic reaction so that the summed ΔG∘ is negative.
d) Two exothermic reactions are run together in order to release the maximum possible heat.