Unformatted text preview: erential form.
Clausius realized in 1865 that he had discovered a new thermodynamic
property, and he chose to name this property entropy. It is designated S and is
T dS (kJ/K) (7–4) int rev Entropy is an extensive property of a system and sometimes is referred to as
total entropy. Entropy per unit mass, designated s, is an intensive property and
has the unit kJ/kg · K. The term entropy is generally used to refer to both total
entropy and entropy per unit mass since the context usually clarifies which
one is meant.
The entropy change of a system during a process can be determined by integrating Eq. 7–4 between the initial and the final states:
2 S ∆S = S2 – S1 = 0.4 kJ/K
0.7 S1 1 Q
T (kJ/K) (7–5) int rev Notice that we have actually defined the change in entropy instead of entropy
itself, just as we defined the change in energy instead of the energy itself when
we developed the first-law relation. Absolute values of entropy are determined
on the basis of the third law of thermodynamics, which is discussed later...
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