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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The “filmstrip” represents five molecular scenes of a gaseous mixture as it reaches equilibrium over time:

$\mathrm{X}$ is purple and $\mathrm{Y}$ is orange: $\mathrm{X}_{2}(g)+\mathrm{Y}_{2}(g) \rightleftharpoons 2 \mathrm{XY}(g)$

(a) Write the reaction quotient, $Q,$ for this reaction.

(b) If each particle represents $0.1 \mathrm{mol},$ find $Q$ for each scene.

(c) If $K>1,$ is time progressing to the right or to the left? Explain.

(d) Calculate $K$ at this temperature.

(e) If $\Delta H_{\mathrm{rxn}}^{\circ}<0,$ which scene, if any, best represents the mixture at a higher temperature? Explain.

(f) Which scene, if any, best represents the mixture at a higher pressure (lower volume)? Explain.

For each reaction, calculate $\Delta H_{\mathrm{rxn}}^{\mathrm{o}}, \Delta S_{\mathrm{rm}}^{\circ}$ and $\Delta G_{\mathrm{rxn}}^{\circ}$ at $25^{\circ} \mathrm{C}$ and state whether or not the reaction is spontaneous. If the reaction is not spontaneous, would a change in temperature make it spontaneous? If so, should the temperature be raised or lowered from $25^{\circ} \mathrm{C} ?$

\begin{equation}\begin{array}{l}{\text { a. } 2 \mathrm\ {CH}_{4}(g) \longrightarrow \mathrm{C}_{2} \mathrm{H}_{6}(g)+\mathrm{H}_{2}(g)} \\ {\text { b. } 2 \mathrm\ {NH}_{3}(g) \longrightarrow \mathrm{N}_{2} \mathrm{H}_{4}(g)+\mathrm{H}_{2}(g)} \\ {\text { c. } \mathrm{N}_{2}(g)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm\ {NO}(g)} \\ {\text { d. } 2 \mathrm\ {KClO}_{3}(s) \longrightarrow 2 \mathrm\ {KCl}(s)+3 \mathrm{O}_{2}(g)}\end{array}\end{equation}