9.10 Entropy

The quantity dQ/T is called the change of entropy. Thus in any thermodynamic process, when any quantity of heat dQ is given out by a substance at absolute temperature T, the entropy of the substance is reduced by dQ/T. Since the quantity of heat dQ absorbed or emitted in any thermodynamic process depends on the mass and specific heat of the substance, the entropy depends on the mass and nature of the substance emitting or absorbing heat. As a result, the entropy of a substance is reckoned per unit mass of the substance and it is different for different substances.

As in dealing with internal energy, we take an arbitrary starting point at which the entropy of a substance is taken a zero; what we are concerned with is not the absolute ...

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