Concise Physical Chemistry

c05 JWBS043-Rogers September 13, 2010 11:25 Printer Name: Yet to Come

5 Entropy and the Second Law

The second law of thermodynamics and the concept of entropy are firmly based on

Sadi Carnot’s somewhat abstract demonstration that the work done by drawing heat

from a hot reservoir and expelling it to a cold reservoir is independent of the nature of

the engine that carries out the work (Fig. 5.1). An especially readable description of

the progression of Carnot’s abstract reflections on the efficiency of steam engines to

the form of the entropy function we use today was given by Kondipudi and Prigogine

(1998). We shall not follow the historical development of this idea, interesting though

it is; rather we shall jump right to Clausius’s definition of the entropy, Ludwig

Boltzmann’s statistical interpretation, and the influence of the second law on physical

phenomena and chemical reactions.

5.1 ENTROPY

In 1865, Rudolf Clausius showed that the cyclic integral

∮

dq/Tis zero for an

abstract Carnot engine operatingreversiblyaround a cyclic path:

∮

dq

T

= 0

Thus the integrand, which Clausius namedentropyand gave the symboldS,is

athermodynamic function. This definition is one statement of the second law of

Concise Physical Chemistry,by Donald W. Rogers

Copyright©C2011 John Wiley & Sons, Inc.

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