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Unformatted text preview: sing that the entropy of a substance is lowest in the solid phase and highest
in the gas phase (Fig. 7–20). In the solid phase, the molecules of a substance
continually oscillate about their equilibrium positions, but they cannot move
relative to each other, and their position at any instant can be predicted with
good certainty. In the gas phase, however, the molecules move about at random, collide with each other, and change direction, making it extremely difficult to predict accurately the microscopic state of a system at any instant.
Associated with this molecular chaos is a high value of entropy.
When viewed microscopically (from a statistical thermodynamics point of
view), an isolated system that appears to be at a state of equilibrium may exhibit a high level of activity because of the continual motion of the molecules.
To each state of macroscopic equilibrium there corresponds a large number of
possible microscopic states or molecular configurations. The entropy of a
system is related to the total number of possible microscopic states of that
system, called thermodynamic probability p, by the Boltzmann relation, expressed as
S k ln p (7–20) where k 1.3806 10 23 J/K is th...
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This document was uploaded on 11/28/2012.
- Spring '09