Which of the following can be determined about ∆So for the reaction?

Question

A student conducts a reaction at 298 K in a rigid vessel and the reaction goes to completion. The temperature of the reaction vessel drops during the reaction. Which of the following can be determined about ∆S^o for the reaction?

1. ∆S^o < 0 at 298 K, since ∆H < 0 and ∆G > 0.
2. ∆S o < 0, since the reaction goes nearly to completion at 298 K.,
3. ∆S^o > 0, since the reaction is thermodynamically unfavorable at 298 K
4. ∆S^o > 0, since the reaction is thermodynamically favorable at 298 K.

Answer 1

As the reaction went to completion, ΔG < 0. The reaction is endothermic as the vessel cooled, so ΔH is positive.

From the relation ΔG = ΔH -TΔS, if ΔG is < 0 and ΔH is > 0 then ΔS must be > 0, so the fourth choice seems to be correct, ∆S^o > 0, since the reaction is thermodynamically favorable at 298 K.