91Ó°ÊÓ

In the process of respiration, glucose is oxidized completely. In fermentation, ${\mathbf{O}}_{\mathbf{2}}$is absent and glucose is broken down to ethanol and ${\mathbf{CO}}_{\mathbf{2}}$. Ethanol is oxidized to ${\mathbf{CO}}_{\mathbf{2}}$and ${\mathbf{H}}_{\mathbf{2}}\mathbf{O}$.

Respiration:${\mathbf{C}}_{\mathbf{6}}{\mathbf{H}}_{\mathbf{12}}{\mathbf{O}}_{\mathbf{6}}\mathbf{\left(}\mathbf{s}\mathbf{\right)}\mathbf{+}{\mathbf{O}}_{\mathbf{2}}\mathbf{\left(}\mathbf{g}\mathbf{\right)}\mathbf{→}{\mathbf{CO}}_{\mathbf{2}}\mathbf{\left(}\mathbf{g}\mathbf{\right)}\mathbf{+}{\mathbf{H}}_{\mathbf{2}}\mathbf{O}\mathbf{\left(}\mathbf{l}\mathbf{\right)}$

Fermentation:${\mathbf{C}}_{\mathbf{6}}{\mathbf{H}}_{\mathbf{12}}{\mathbf{O}}_{\mathbf{6}}\mathbf{\left(}\mathbf{s}\mathbf{\right)}\mathbf{→}{\mathbf{C}}_{\mathbf{2}}{\mathbf{H}}_{\mathbf{5}}\mathbf{OH}\mathbf{\left(}\mathbf{l}\mathbf{\right)}\mathbf{+}\mathbf{C}{\mathbf{O}}_{\mathbf{2}}\mathbf{\left(}\mathbf{g}\mathbf{\right)}$

Ethanol oxidation:${\mathbf{C}}_{\mathbf{2}}{\mathbf{H}}_{\mathbf{5}}\mathbf{OH}\mathbf{\left(}\mathbf{l}\mathbf{\right)}\mathbf{+}{\mathbf{O}}_{\mathbf{2}}\mathbf{\left(}\mathbf{g}\mathbf{\right)}\mathbf{→}{\mathbf{CO}}_{\mathbf{2}}\mathbf{\left(}\mathbf{g}\mathbf{\right)}\mathbf{+}{\mathbf{H}}_{\mathbf{2}}\mathbf{O}\mathbf{\left(}\mathbf{l}\mathbf{\right)}$

1. Calculate ${\mathbf{Δ³Ò}}_{\mathbf{rxn}}^{\mathbf{o}}$for respiration of $\mathbf{1}\mathbf{.}\mathbf{00}\mathbf{g}$glucose.
2. Calculate ${\mathbf{Δ³Ò}}_{\mathbf{rxn}}^{\mathbf{o}}$for fermentation of $\mathbf{1}\mathbf{.}\mathbf{00}\mathbf{g}$glucose.
3. Calculate ${\mathbf{Δ³Ò}}_{\mathbf{rxn}}^{\mathbf{o}}$for oxidation of the ethanol from part (c).

Which of the following processes are spontaneous?

(a) Methane burns in air.

(b) A teaspoonful of sugar dissolves in a cup of hot coffee.

(c) A soft-boiled egg becomes raw.

Distinguish between the terms spontaneous and instantaneous. Give an example of a process that is spontaneous but very slow, and one that is very fast but not spontaneous.

Distinguish between the terms spontaneous and nonspontaneous. Can a nonspontaneous process occur? Explain.

(a) Is an endothermic reaction more likely to be spontaneous at higher temperatures or lower temperatures? Explain.

(b) The change depicted below occurs at constant pressure. Explain your answers to each of the following:

(1) What is the sign of $\mathbf{Δ\pm á}$?

(2) What is the sign of $\mathbf{Δ³\S }$?

(3) What is the sign of ${\mathbf{Δ³\S }}_{\mathbf{surr}}$?

(4) How does the sign of$\mathbf{Δ³Ò}$vary with temperature?

Use Appendix B to determine the${\mathbf{\text{K}}}_{\mathbf{\text{sp}}}$of${\mathbf{\text{CaF}}}_{\mathbf{\text{2}}}$

Is each statement true or false? If false, correct it.

(a) All spontaneous reactions occur quickly.

(b) The reverse of a spontaneous reaction is nonspontaneous.

(c) All spontaneous processes release heat.

(d) The boiling of water at ${\mathbf{100}}^{\mathbf{°}}\mathbf{\text{C}}$and 1 atm is spontaneous.

(e) If a process increases the freedom of motion of the particles of a system, the entropy of the system decreases.

(f) The energy of the universe is constant; the entropy of the universe decreases toward a minimum.

(g) All systems disperse their energy spontaneously.

(h) Both$\mathit{Δ}{\mathit{S}}_{\mathbf{\text{sys}}}$androle="math" localid="1663321957929" $\mathit{Δ}{\mathit{S}}_{\mathbf{\text{surr}}}$equal zero at equilibrium.

Propylene (propene;${\mathbf{\text{CH}}}_{\mathbf{\text{3}}}{\mathbf{\text{CH = CH}}}_{\mathbf{\text{2}}}$ ) is used to produce polypropylene and many other chemicals. Although most is obtained from the cracking of petroleum, about$\mathbf{2}\mathbf{\%}$ is produced by catalytic dehydrogenation of propane ( ${\mathbf{\text{CH}}}_{\mathbf{\text{3}}}{\mathbf{\text{CH}}}_{\mathbf{\text{2}}}{\mathbf{\text{CH}}}_{\mathbf{\text{3}}}$):

${\mathbf{\text{CH}}}_{\mathbf{\text{3}}}{\mathbf{\text{CH}}}_{\mathbf{\text{2}}}\mathbf{\text{C}}{\mathbf{\text{H}}}_{\mathbf{\text{3}}}\stackrel{{\mathbf{\text{Pt/Al}}}_{\mathbf{\text{2}}}{\mathbf{\text{O}}}_{\mathbf{\text{3}}}}{\mathbf{→}}{\mathbf{\text{CH}}}_{\mathbf{\text{3}}}{\mathbf{\text{CH = CH}}}_{\mathbf{\text{2}}}{\mathbf{\text{+H}}}_{\mathbf{\text{2}}}$

Because this reaction is endothermic, heaters are placed between the reactor vessels to maintain the required temperature.

(a) If the molar entropy${\mathit{S}}^{\mathbf{°}}$, , of propylene is$\mathbf{\text{267.1 J/molK}}$ , find its entropy of formation, ${\mathbf{\text{S}}}_{\mathbf{\text{f}}}^{\mathbf{\text{o}}}$.

(b) Find $\mathbf{∆}{\mathit{G}}_{\mathbf{f}}^{\mathbf{°}}$of propylene ($\mathbf{∆}{\mathit{H}}_{\mathbf{f}}^{\mathbf{°}}$for propylene$\mathbf{\text{= 20.4 kJ/mol}}$).

(c) Calculate $\mathbf{∆}{\mathit{H}}_{\mathbf{r}\mathbf{x}\mathbf{n}}^{\mathbf{°}}$ and$\mathbf{∆}{\mathit{G}}_{\mathbf{r}\mathbf{x}\mathbf{n}}^{\mathbf{°}}$ for the dehydrogenation.

(d) What is the theoretical yield of propylene at $\mathbf{580}\mathbf{°}\mathit{C}$ if the initial pressure of propane is $\mathbf{1}\mathbf{.}\mathbf{00}\mathit{a}\mathit{t}\mathit{m}$?

(e) Would the yield change if the reactor walls were permeable to${\mathit{H}}_{\mathbf{2}}$ ? Explain.

(f) At what temperature is the dehydrogenation spontaneous, with all substances in the standard state?