Final answer:
The expression for ΔGrxn at temperatures other than 25 °C, assuming negligible changes in ΔH°rxn and ΔS°rxn, is ΔGrxn = ΔH°rxn - TΔS°rxn.
Step-by-step explanation:
At temperatures other than 25 °C, assuming the change in ΔH°rxn (standard enthalpy change) and ΔS°rxn (standard entropy change) is negligible, the expression for ΔGrxn (standard Gibbs free energy change) is ΔGrxn = ΔH°rxn - TΔS°rxn. Therefore, the correct answer is a) ΔH°rxn - TΔS°rxn. This relationship is derived from the fundamental Gibbs free energy equation at any temperature when the enthalpy and entropy of a reaction are assumed to be temperature independent.