Free energy

A. Decreases in all spontaneous (or irreversible) processes

B. Change during a spontaneous process has a negative value

C. Remains unchanged in reversible processes carried at constant temperature and pressure

D. All of the above

Answer: Option D

Solution(By Examveda Team)

Since for an spontaneous process $$s > dU + PdV$$
For, constant temperature and constant pressure process the above equation can be written as
$$\eqalign{ & d\left( {TS - U} \right) > PdV \cr & \Rightarrow d\left( { - A} \right) > PdV \cr & \Rightarrow {\left( {dG} \right)_{T,P}} < 0. \cr} $$
For spontaneous process (irreversible). And $${\left( {dG} \right)_{T,P}} = 0$$   for, a reversible process.