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General Chemistry Principles, Patterns, and Applications, 2011

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a. What is ΔS for this process?<br />

b. Which is the more highly ordered form of sulfur—S α or S β?<br />

Answer:<br />

a. 1.09 J/(mol·K)<br />

b. S α<br />

Summary<br />

A measure of the disorder of a system is its entropy (S), a state function whose value increases with an<br />

increase in the number of available microstates. Areversible process is one for which all intermediate<br />

states between extremes are equilibrium states; it can change direction at any time. In contrast,<br />

anirreversible process occurs in one direction only. The change in entropy of the system or the<br />

surroundings is the quantity of heat transferred divided by the temperature. The second law of<br />

thermodynamics states that in a reversible process, the entropy of the universe is constant, whereas in<br />

an irreversible process, such as the transfer of heat from a hot object to a cold object, the entropy of the<br />

universe increases.<br />

K E Y T A K E A W A Y S<br />

<br />

<br />

For a given system, the greater the number of microstates, the higher the entropy.<br />

During a spontaneous process, the entropy of the universe increases.<br />

K E Y E QU A T I ON<br />

Entropy change<br />

Equation 18.15<br />

: DS = qrevT<br />

C O N C E PTUAL P R OBLEMS<br />

1. A Russian space vehicle developed a leak, which resulted in an internal pressure drop from 1 atm to 0.85 atm.<br />

Is this an example of a reversible expansion? Has work been done?<br />

2. Which member of each pair do you expect to have a higher entropy? Why?<br />

a. solid phenol or liquid phenol<br />

b. 1-butanol or butane<br />

c. cyclohexane or cyclohexanol<br />

d. 1 mol of N 2 mixed with 2 mol of O 2 or 2 mol of NO 2<br />

Saylor URL: http://www.saylor.org/books<br />

Saylor.org<br />

1646

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