Clausius realized in 1865 that he had discovered a

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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 defined as Q 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 Irreversible process 2 1 Reversible process 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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