For an adiabatically isolated system the entropy of the system can
never decrease.
But, a more practically useful form of the second law is:
for a system in equilibrium with an environment at a given temperature and pressure the Gibbs free energy, G = U + PV-T S, can never increase.
Consequently, in the equilibrium state of any system (whether a folded protein or a superconductor) the Gibbs free energy must be a minimum.
Never forget this! This is the most important idea in all of thermodynamics!
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Hey Ross,
ReplyDeleteJust trying to grasp your first statement and I was wondering if entropy of an adiabaticlly isolated system can never decrease, can it increase? If so the process by which it increases must be irreversible otherwise reversing it would result in a decrease of entropy.
Hope I'm making sense,
Michael.
@Michael: The entropy can increase, or remain constant. Good insight on the reversibility - you can actually use this to form a definition of an irreversible process.
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