My previous post made reference to the second law of thermodynamics. I've had a couple of discussions in the pub with people about this recently, trying to think what the three laws are. I don't think we ever managed it, mainly because there are actually four laws. It's no wonder we could never agree on them. So here, for reference are the "three laws of thermodynamics", taken from Scienceworld:
Zeroth Law: If two systems are in thermal equilibrium with a third system, then they must be in thermal equilibrium with each other.
First Law: Energy is conserved
Second Law: it is impossible for a system operating in a cycle to produce positive heat flow from a colder body to a hotter body.
Third Law: As temperature goes to 0, the entropy S approaches a constant. Furthermore, it guarantees that the entropy of a pure, perfectly crystalline substance is 0 if the absolute temperature is 0.
I think it is the second of these that leads to entropy tending to increase over time.
So in summary: For energy E, temperature T, pressure P, and volume V, with entropy S dE - T.dS + P.dV <= 0 .
Hopefully this will be the end of that one...
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