A chemist is comparing the thermodynamic behavior of four hypothetical reactions (A–D). The enthalpy and entropy changes for each reaction are listed below.
Reaction A ΔH<0ΔS>0
Reaction B ΔH<0ΔS<0
Reaction C ΔH>0ΔS>0
Reaction D ΔH>0ΔS<0
Assume that the magnitudes of ΔH and ΔS for a given reaction are temperature-independent over the range considered.
(1) Part 1: For Reaction A, describe whether the reaction is spontaneous, non-spontaneous, or at equilibrium at any temperature. Justify your answer with thermodynamic reasoning.
(2) Part 2: For Reaction B, predict how the sign of ΔG depends on temperature. State whether the reaction is thermodynamically favored at (i) very low temperatures and (ii) very high temperatures, and explain your reasoning.
(3) Part 3: For Reaction C, repeat the analysis from part (b). Discuss spontaneity in the low-temperature and high-temperature limits.
(4) Part 4: For Reaction D, explain why the reaction is never thermodynamically favored at any temperature. Support your answer qualitatively.