Does entropy in a closed system always increase OR remain constant (

[srfriggen]

Does entropy in a closed system always increase OR remain constant ( in equilibrium ).

I have a friend arguing it is ALWAYS increasing.

His latest argument was, "if no energy enters or leaves an isolated system, the availability of the remaining energy decreases."

 

[ofirg]

Once the closed system reaches its final equilibrium state , the entropy remains constant. The entropy of a system is a function of several macroscopic quantitates ( Energy, Volume, Number of particles ). Once all this remains constant ( Like a gas in a box which is uniformally distributed in it) how could the entropy change?