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Chapter 17: Problem 5

How does the entropy of a system change for each of the following processes? (a) A solid melts. (b) A liquid freezes. (c) A liquid boils. (d) A vapor is converted to a solid. (e) A vapor condenses to a liquid. (f) A solid sublimes. (g) Urea dissolves in water.

Short Answer

Expert verified
The entropy changes for the processes are: (a) Increases (b) Decreases (c) Increases (d) Decreases (e) Decreases (f) Increases (g) Increases

Step by step solution

01

Entropy change in melting or freezing

For (a) A solid melts, and (b) A liquid freezes, the concept of phase transition applies. When a solid melts and becomes a liquid, the order of the system decreases (becomes disordered), thus the entropy increases. Conversely, when a liquid freezes and becomes a solid, the order of the system increases (becomes ordered), thus the entropy decreases.
02

Entropy change in boiling, condensation, and sublimation

For (c) A liquid boils, (d) A vapor condenses to a liquid, (e) A vapor is converted to a solid, and (f) A solid sublimes, the phase change concept also applies here. In boiling, a liquid becomes a gas, which is a conversion to a more chaotic state, hence the entropy increases. Condensation, which is a conversion from gas to liquid, and from gas to solid, leads to more orderly states, so the entropy decreases here. For sublimation, a solid is directly becoming gas, which is an enormous increase in disorder, so entropy increases tremendously.
03

Entropy change in dissolving process

For (g) Urea dissolves in water, when a solid dissolves in a liquid, it increases the disorder of the system. Hence, the entropy increases when urea dissolves in water.

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Most popular questions from this chapter

The equilibrium constant \(\left(K_{P}\right)\) for the reaction $$ \mathrm{H}_{2}(g)+\mathrm{CO}_{2}(g) \rightleftharpoons \mathrm{H}_{2} \mathrm{O}(g)+\mathrm{CO}(g) $$ is 4.40 at \(2000 \mathrm{~K}\). (a) Calculate \(\Delta G^{\circ}\) for the reaction. (b) Calculate \(\Delta G\) for the reaction when the partial pressures are \(P_{\mathrm{H}_{2}}=0.25 \mathrm{~atm}, P_{\mathrm{CO}_{2}}=0.78 \mathrm{~atm}\) \(P_{\mathrm{H}_{2} \mathrm{O}}=0.66 \mathrm{~atm},\) and \(P_{\mathrm{CO}}=1.20 \mathrm{~atm}\)

Consider the following reaction at \(25^{\circ} \mathrm{C}\) : $$ \mathrm{Fe}(\mathrm{OH})_{2}(s) \rightleftharpoons \mathrm{Fe}^{2+}(a q)+2 \mathrm{OH}^{-}(a q) $$ Calculate \(\Delta G^{\circ}\) for the reaction. \(K_{\mathrm{sp}}\) for \(\mathrm{Fe}(\mathrm{OH})_{2}\) is \(1.6 \times 10^{-14}\)

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?

Consider the reaction \(\mathrm{A} \longrightarrow \mathrm{B}+\mathrm{C}\) at \(298 \mathrm{~K}\). Given that the forward rate constant \(\left(k_{f}\right)\) is \(0.46 \mathrm{~s}^{-1}\) and the reverse rate constant \(\left(k_{r}\right)\) is \(1.5 \times 10^{-2} / M \cdot \mathrm{s},\) calculate \(\Delta G^{\circ}\) of the reaction.
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