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Problem 107

In the process of respiration, glucose is oxidize…

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Problem 111

Synthesis gas, a mixture that includes the fuels CO and $\mathrm{H}_{2}$, is used to produce liquid hydrocarbons and methanol. It is made at pressures up to 100 atm by oxidation of methane followed by the steam reforming and water-gas shift reactions. Because the process is exothermic, temperatures reach $950-1100^{\circ} \mathrm{C}$, and the conditions are such that the amounts of $\mathrm{H}_{2}, \mathrm{CO}, \mathrm{CO}_{2}, \mathrm{CH}_{4}$, and $\mathrm{H}_{2} \mathrm{O}$ leaving the reactor are close to the equilibrium amounts for the steam re-forming and water-gas shift reactions:
$$\begin{aligned} \mathrm{CH}_{4}(g)+\mathrm{H}_{2} \mathrm{O}(g) & \rightleftharpoons \mathrm{CO}(g)+3 \mathrm{H}_{2}(g) \quad \text { (steam re-forming) } \\ \mathrm{CO}(g)+\mathrm{H}_{2} \mathrm{O}(g) & \rightleftharpoons \mathrm{CO}_{2}(g)+\mathrm{H}_{2}(g) \quad \text { (water-gas shift) } \end{aligned}$$
(a) At $1000 .$ ', what are $\Delta G^{\circ}$ and $\Delta H^{\circ}$ for the steam re-forming
reaction and for the water-gas shift reaction?
(b) By doubling the steam re-forming step and adding it to the water-gas shift step, we obtain the following combined reaction:
$$2 \mathrm{CH}_{4}(g)+3 \mathrm{H}_{2} \mathrm{O}(g) \rightleftharpoons \mathrm{CO}_{2}(g)+\mathrm{CO}(g)+7 \mathrm{H}_{2}(g)$$
Is this reaction spontaneous at $1000 .^{\circ} \mathrm{C}$ in the standard state?
(c) Is it spontaneous at 98 atm and $50 . \%$ conversion (when $50 . \%$ of the starting materials have reacted)?
(d) Is it spontaneous at 98 atm and $90 . \%$ conversion?

LJ

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Problem 106

When heated, the DNA double helix separates into two random coil single strands. When cooled, the random coils reform the double helix: double helix $\Longrightarrow 2$ random coils.
(a) What is the sign of $\Delta S$ for the forward process? Why?
(b) Energy must be added to break $\mathrm{H}$ bonds and overcome dispersion forces between the strands. What is the sign of $\Delta G$ for the forward process when $T \Delta S$ is smaller than $\Delta H ?$
(c) Write an expression for $T$ in terms of $\Delta H$ and $\Delta S$ when the reaction is at equilibrium. (This temperature is called the melting temperature of the nucleic acid.)

Answer
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Chapter 20
Thermodynamics: Entropy, Free Energy, and the Direction of Chemical Reactions
CHEMISTRY: The Molecular Nature of Matter and Change 2016

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