Question

Show that at thermal equilibrium the temperature and pressure of the body are the same as those of the environment. At thermal equilibrium ∆A = 0, and ∆G = 0 .

Answer 1

We know that Helmholtz free energy (A) = U - TS where

U = internal energy

T = Temperature

S = Entropy

Now at constant T and P, i.e when the system and surrounding left in contact with each other over a period of time then all the variables would be almost of the same value.

Therefore the change in A will be negligible or zero.

For Gibbs free energy (G ) = U - TS + PV

The T and P will make the other variables constant over a certain period of time, Hence the change in G will be zero.