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Ch.18 - Free Energy and Thermodynamics
All textbooksTro 4th EditionCh.18 - Free Energy and ThermodynamicsProblem 99
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Chapter 18, Problem 99

Is the sign of ΔSuniv for each process positive or negative? Explain for the following: b. the electrolysis of H2O(l) to H2(g) and O2(g) at 298 K c. the growth of an oak tree from a little acorn.

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<insert step 1> Identify the processes involved in each scenario. For part b, the process is the electrolysis of water, and for part c, it is the growth of an oak tree from an acorn.>
<insert step 2> Recall the second law of thermodynamics, which states that the entropy of the universe (ΔS_{univ}) increases for spontaneous processes.>
<insert step 3> For part b, consider the electrolysis of water: 2H_2O(l) \rightarrow 2H_2(g) + O_2(g). This process involves breaking bonds in water molecules to form hydrogen and oxygen gases, which increases the disorder or entropy of the system.>
<insert step 4> For part c, consider the growth of an oak tree: This process involves organizing simple molecules into complex structures, which decreases the entropy of the system. However, the overall entropy change of the universe must be considered, including the surroundings.>
<insert step 5> Determine the sign of ΔS_{univ} for each process by considering the changes in entropy of the system and surroundings. For part b, the increase in gas molecules suggests a positive ΔS_{univ}. For part c, the decrease in system entropy is offset by energy exchanges with the surroundings, potentially leading to a positive ΔS_{univ} if the process is spontaneous.>
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Textbook Question

The values of ΔG°f for the hydrogen halides become less negative with increasing atomic number. The ΔG°f of HI is slightly positive. However, the trend in ΔS°f is to become more positive with increasing atomic number. Explain.

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Open Question

Consider the reaction X2(g) → 2X(g). When a vessel initially containing 755 torr of X2 comes to equilibrium at 298 K, the equilibrium partial pressure of X is 103 torr. The same reaction is repeated with an initial partial pressure of 748 torr of X2 at 755 K; the equilibrium partial pressure of X is 532 torr. Find ΔH° for the reaction.

Textbook Question

Dinitrogen tetroxide decomposes to nitrogen dioxide: N2O4(g) → 2 NO2(g) ΔH°rxn = 55.3 kJ At 298 K, a reaction vessel initially contains 0.100 atm of N2O4. When equilibrium is reached, 58% of the N2O4 has decomposed to NO2. What percentage of N2O4 decomposes at 388 K? Assume that the initial pressure of N2O4 is the same (0.100 atm).

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Textbook Question

Indicate and explain the sign of ΔSuniv for each process. a. 2 H2(g) + O2(g) → 2 H2O (l) at 298 K.

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Open Question

The Haber process is very important for agriculture because it converts N2(g) from the atmosphere into bound nitrogen, which can be taken up and used by plants. The Haber process reaction is N2(g) + 3 H2(g) → 2 NH3(g). The reaction is exothermic but is carried out at relatively high temperatures. Why?

Textbook Question

A metal salt with the formula MCl2 crystallizes from water to form a solid with the composition MCl2 • 6 H2O. The equilibrium vapor pressure of water above this solid at 298 K is 18.3 mmHg. What is the value of ΔG for the reaction MCl2 • 6 H2O(s) ⇌ MCl2(s) + 6 H2O(g) when the pressure of water vapor is 18.3 mmHg? When the pressure of water vapor is 760 mmHg?

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