In an isothermal process, the change in entropy (delta-S) is the change in heat (Q) divided by the absolute temperature (T):
delta-S = Q/TIn any reversible thermodynamic process, it can be represented in calculus as the integral from a processes initial state to final state of dQ/T.
The SI units of entropy are J/K (joules/degrees Kelvin).
Entropy & The Second Law of ThermodynamicsOne way of stating the second law of thermodynamics is:
In any closed system, the entropy of the system will either remain constant or increase.One way to view this is that adding heat to a system causes the molecules and atoms to speed up. It may be possible (though tricky) to reverse the process in a closed system (i.e. without drawing any energy from or releasing energy somewhere else) to reach the initial state, but you can never get the entire system "less energetic" than it started ... the energy just doesn't have anyplace to go.