A chemical reaction, such as HI forming from its elements, can reach equilibrium at many temperatures. In contrast, a phase change, such as ice melting, is in equilibrium at a given pressure and temperature. Each of the graphs below depicts $G_{\mathrm{sys}}$ vs. extent of change. (a) Which graph depicts how $G_{\mathrm{sys}}$ changes for the formation of HI? Explain. (b) Which graph depicts how $G_{\mathrm{sys}}$ changes as ice melts at 18C and 1 atm? Explain.

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Calculate $\Delta G_{\mathrm{rn}}^{\circ}$ for the reaction:

$$\mathrm{CaCO}_{3}(s) \longrightarrow \mathrm{CaO}(s)+\mathrm{CO}_{2}(g)$$

Use the following reactions and given $\Delta G_{\mathrm{ren}}^{\circ}$ values:

$$\begin{array}{l}{\mathrm{Ca}(s)+\mathrm{CO}_{2}(g)+\frac{1}{2} \mathrm{O}_{2}(g) \longrightarrow \mathrm{CaCO}_{3}(s) \quad \Delta G_{\mathrm{rm}}^{\circ}=-734.4 \mathrm{kJ}} \\ {2 \mathrm{Ca}(s)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{CaO}(s)} \quad\quad\quad\quad\quad\quad \Delta G_{\mathrm{rxn}}^{\circ}=-1206.6 \mathrm{kJ}\end{array}$$

Calculate the equilibrium constant at $25^{\circ} \mathrm{C}$ for each of the following reactions from the value of $\Delta G^{\circ}$ given.

(a) $\mathrm{I}_{2}(s)+\mathrm{Cl}_{2}(g) \longrightarrow 2 \mathrm{ICl}(g) \quad \Delta G^{\circ}=-10.88 \mathrm{kJ}$

(b) $\mathrm{H}_{2}(g)+\mathrm{I}_{2}(s) \rightarrow 2 \mathrm{HI}(g) \quad \Delta G^{\circ}=3.4 \mathrm{kJ}$

(c) $\mathrm{CS}_{2}(g)+3 \mathrm{Cl}_{2}(g) \longrightarrow \mathrm{CCl}_{4}(g)+\mathrm{S}_{2} \mathrm{Cl}_{2}(g) \quad \Delta G^{\circ}=-39 \mathrm{kJ}$

(d) $2 \mathrm{SO}_{2}(g)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{SO}_{3}(g) \quad \Delta G^{\circ}=-141.82 \mathrm{kJ}$

(e) $\mathrm{CS}_{2}(g) \rightarrow \mathrm{CS}_{2}(l) \qquad \Delta G^{\circ}=-1.88 \mathrm{kJ}$