[chrisaltman]

Hello all,
Quick question: I was given a problem in my GenChemII course.
Essentially, it was as follows:
The A form of a compound is converted into the less dense B form in preparation of an ore.
Use the data provided to calculate the lowest temperature at which the conversion is feasible.

(Delta)Hf (kj/mol) of A-compound: -3055 // S value: 129.3
(Delta)Hf (kj/mol) of B-compound: -3027 // S value: 154.4

I understand that when (Delta)G=0, the reaction is at equilibrium,
but why does that enable us to use the free energy change equation for the transition?
The transition state is at equilibrium, but does that lead us to the assumption
that the B-form of compound is now present?

[Schrödinger]

The fact that $$\Delta{G}=0 /$$ at equilibrium hints at the direction in which the reaction will proceed if the temperature is increased or decreased. But you don't have to use $$\Delta{G}=0 /$$ for the transition in order to calculate the minimum temperature at which the reaction is spontaneous.

Instead solve the inequality $$\Delta{G}<0 /$$
i.e., $$ \Delta{H} -T\Delta{S} < 0 /$$
i.e., $$ \Delta{H} < T\Delta{S} /$$
This one's easier to understand