Textbook Question 4J.15

[Sabrina Camua 2J]

Hello I could use some assistance in answering/approaching this question:
Which of the following compounds become less stable with respect to the elements as the temperature is raised:
(a) PCl5 (g)
(b) HCN (g)
(c) NO (g)
(d) SO2 (g)?

[Chem_Mod]

Less stable = positive G
G = H - TS


Increasing the temperature can only make G positive if Delta[/tex]S is negative

Using appendix 2A, look up the molar entropies for each species. Remember that entropy is not zero for the elements. For example, for NO we set up the formation reaction
1/2 N₂ (g) + 1/2 O₂ (g) NO (g)

You would then calculate S for this reaction by finding the molar entropy of NO (g) and subtracting the molar entropy of N₂ (g) and O₂ (g), each multiplied by 0.5 because of their stoichiometry in the formation reaction.