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Chapter 17: Problem 8

State the third law of thermodynamics and explain its usefulness in calculating entropy values.

Short Answer

Expert verified
The third law of thermodynamics states that the entropy of a perfect crystal at absolute zero is exactly zero. It is useful in calculating entropy as it provides a baseline or reference point (zero entropy for a perfect crystal at absolute zero) for determining the entropy of other substances at different temperatures.

Step by step solution

01

State the third law of thermodynamics

The third law of thermodynamics states that the entropy of a perfect crystal at absolute zero is exactly equal to zero. Here, 'absolute zero' refers to zero Kelvin or -273.15°C.
02

Explain entropy

Entropy is a measure of disorder or randomness in a system. It is denoted by \(S\). When a system moves from a very orderly state to a less orderly state, the entropy increases.
03

Explain the relation to calculation of entropy values

The third law of thermodynamics provides a reference point whereby scientists can calculate the entropy of any substance at any temperature. By finding out the entropy value of a system at absolute zero, scientists can then calculate the entropy value of the system at any given temperature. The law, in essence, sets the minimum limit for entropy at absolute zero for a perfect crystalline substance; any other state or substance at any temperature would have higher entropy.

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Most popular questions from this chapter

Carbon monoxide (CO) and nitric oxide (NO) are polluting gases contained in automobile exhaust. Under suitable conditions, these gases can be made to react to form nitrogen \(\left(\mathrm{N}_{2}\right)\) and the less harmful carbon dioxide \(\left(\mathrm{CO}_{2}\right)\). (a) Write an equation for this reaction. (b) Identify the oxidizing and reducing agents. (c) Calculate the \(K_{P}\) for the reaction at \(25^{\circ} \mathrm{C}\). (d) Under normal atmospheric conditions, the partial pressures are \(P_{\mathrm{N}_{2}}=0.80 \mathrm{~atm}, P_{\mathrm{CO}_{2}}=3.0 \times 10^{-4} \mathrm{~atm}\) \(P_{\mathrm{CO}}=5.0 \times 10^{-5} \mathrm{~atm},\) and \(P_{\mathrm{NO}}=5.0 \times 10^{-7} \mathrm{~atm}\) Calculate \(Q_{P}\) and predict the direction toward which the reaction will proceed. (e) Will raising the temperature favor the formation of \(\mathrm{N}_{2}\) and \(\mathrm{CO}_{2} ?\)

Define entropy. What are the units of entropy?

Which of the following is not accompanied by an increase in the entropy of the system: (a) mixing of two gases at the same temperature and pressure, (b) mixing of ethanol and water, (c) discharging a battery, (d) expansion of a gas followed by compression to its original temperature, pressure, and volume?

For a reaction with a negative \(\Delta G^{\circ}\) value, which of the following statements is false? (a) The equilibrium constant \(K\) is greater than one. (b) The reaction is spontaneous when all the reactants and products are in their standard states. (c) The reaction is always exothermic.

Crystallization of sodium acetate from a supersaturated solution occurs spontaneously (see Section 12.1). What can you deduce about the signs of \(\Delta S\) and \(\Delta H ?\)
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