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Ch.19 - Free Energy & Thermodynamics
All textbooksTro 6th EditionCh.19 - Free Energy & ThermodynamicsProblem 58d
Chapter 19, Problem 58d

Use data from Appendix IIB to calculate ΔS°rxn for each of the reactions. In each case, try to rationalize the sign of ΔS°rxn. d. N2O4(g) + 4 H2(g) → N2(g) + 4 H2O(g)

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Identify the standard molar entropy values (S°) for each reactant and product from Appendix IIB.
Write the balanced chemical equation: \( \text{N}_2\text{O}_4(g) + 4 \text{H}_2(g) \rightarrow \text{N}_2(g) + 4 \text{H}_2\text{O}(g) \).
Calculate the total standard entropy of the products: \( S^\circ_{\text{products}} = S^\circ_{\text{N}_2(g)} + 4 \times S^\circ_{\text{H}_2\text{O}(g)} \).
Calculate the total standard entropy of the reactants: \( S^\circ_{\text{reactants}} = S^\circ_{\text{N}_2\text{O}_4(g)} + 4 \times S^\circ_{\text{H}_2(g)} \).
Determine the standard entropy change for the reaction: \( \Delta S^\circ_{\text{rxn}} = S^\circ_{\text{products}} - S^\circ_{\text{reactants}} \).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Entropy (ΔS)

Entropy, represented as ΔS, is a measure of the disorder or randomness in a system. In chemical reactions, changes in entropy can indicate how the arrangement of molecules changes from reactants to products. A positive ΔS suggests an increase in disorder, while a negative ΔS indicates a decrease in disorder.
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Standard Entropy of Formation

The standard entropy of formation is the entropy content of a substance in its standard state, typically at 1 bar of pressure and a specified temperature (usually 298 K). This value is crucial for calculating the overall change in entropy for a reaction, as it allows for the comparison of the entropies of reactants and products.
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Reaction Stoichiometry

Reaction stoichiometry refers to the quantitative relationships between the amounts of reactants and products in a chemical reaction. Understanding stoichiometry is essential for calculating changes in entropy, as it helps determine how many moles of each substance are involved, which directly affects the overall entropy change (ΔS°rxn) for the reaction.
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Related Practice
Textbook Question

Use data from Appendix IIB to calculate ΔS°rxn for each of the reactions. In each case, try to rationalize the sign of ΔS°rxn . a. 3 NO2(g) + H2O(l) → 2 HNO3(aq) + NO(g)

Textbook Question

Use data from Appendix IIB to calculate ΔS°rxn for each of the reactions. In each case, try to rationalize the sign of ΔS°rxn. b. Cr2O3(s) + 3 CO(g) → 2 Cr(s) + 3 CO2(g)

Textbook Question

Use data from Appendix IIB to calculate ΔS°rxn for each of the reactions. In each case, try to rationalize the sign of ΔS°rxn. c. SO2(g) + 1/2 O2(g) → SO3(g)

Textbook Question

Find ΔS° for the formation of CH2Cl2(g) from its gaseous elements in their standard states. Rationalize the sign of ΔS°.

Textbook Question

Methanol (CH3OH) burns in oxygen to form carbon dioxide and water. Write a balanced equation for the combustion of liquid methanol and calculate ΔH°rxn, ΔS°rxn, and ΔG°rxn at 25 °C. Is the combustion of methanol spontaneous?

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Textbook Question

In photosynthesis, plants form glucose (C6H12O6) and oxygen from carbon dioxide and water. Write a balanced equation for photosynthesis and calculate ΔH°rxn, ΔS°rxn, and ΔG°rxn at 25 °C. Is photosynthesis spontaneous?

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