Without using Appendix $\mathrm{B}$ , predict the sign of $\Delta S^{\circ}$ for

(a) $2 \mathrm{K}(s)+\mathrm{F}_{2}(g) \longrightarrow 2 \mathrm{KF}(s)$

(b) $\mathrm{NH}_{3}(g)+\mathrm{HBr}(g) \longrightarrow \mathrm{NH}_{4} \mathrm{Br}(s)$

(c) $\mathrm{NaClO}_{3}(s) \longrightarrow \mathrm{Na}^{+}(a q)+\mathrm{ClO}_{3}^{-}(a q)$

## Discussion

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Which of the following processes are spontaneous and which are nonspontaneous: (a) the ripening of a banana, (b) dissolution of sugar in a cup of hot coffee, (c) the reaction of nitrogen atoms to form $\mathrm{N}_{2}$ molecules at $25^{\circ} \mathrm{C}$ and $1 \mathrm{atm},(\mathbf{d})$ lightning, (e) formation of $\mathrm{CH}_{4}$ and $\mathrm{O}_{2}$ molecules from $\mathrm{CO}_{2}$ and $\mathrm{H}_{2} \mathrm{O}$ at room temperature and 1 atm of pressure?

The evaporation of one mole of water at 298 $\mathrm{K}$ has a standard free energy change of 8.58 $\mathrm{kJ}$ .

$\mathrm{H}_{2} \mathrm{O}(l) \rightleftharpoons \mathrm{H}_{2} \mathrm{O}(g) \quad \Delta G_{298}^{\circ}=8.58 \mathrm{kJ}$

(a) Is the evaporation of water under standard thermodynamic conditions spontaneous?

(b) Determine the equilibrium constant, $K_{P},$ for this physical process.

(c) By calculating $\Delta G,$ determine if the evaporation of water at 298 $\mathrm{K}$ is spontaneous when the partial pressure of water, $P_{\mathrm{H}_{2} \mathrm{O}},$ is 0.011 $\mathrm{atm.}$

(d) If the evaporation of water were always nonspontaneous at room temperature, wet laundry would never dry when placed outside. In order for laundry to dry, what must be the value of $P_{\mathrm{H}_{2}} \mathrm{O}$ in the air?

Consider the reaction 2 $\mathrm{NO}_{2}(g) \longrightarrow \mathrm{N}_{2} \mathrm{O}_{4}(g) .(\mathbf{a})$ Using data from Appendix $\mathrm{C},$ calculate $\Delta G^{\circ}$ at 298 $\mathrm{K}$ . (b) Calculate $\Delta G$ at 298 $\mathrm{K}$ if the partial pressures of $\mathrm{NO}_{2}$ and $\mathrm{N}_{2} \mathrm{O}_{4}$ are 0.40 atm and 1.60 atm, respectively.