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Ch.19 - Free Energy & Thermodynamics
Tro - Chemistry: A Molecular Approach 6th Edition
Tro6th EditionChemistry: A Molecular ApproachISBN: 9780137832217Not the one you use?Change textbook
All textbooksTro 6th EditionCh.19 - Free Energy & ThermodynamicsProblem 57d
Chapter 19, Problem 57d

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. 2 H2S(g) + 3 O2(g) → 2 H2O(l) + 2 SO2(g)

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Identify the standard entropy values (S°) for each reactant and product from Appendix IIB.
Write the balanced chemical equation: 2 H2S(g) + 3 O2(g) → 2 H2O(l) + 2 SO2(g).
Calculate the total standard entropy of the reactants: (2 * S°(H2S)) + (3 * S°(O2)).
Calculate the total standard entropy of the products: (2 * S°(H2O)) + (2 * S°(SO2)).
Determine the change in standard entropy (ΔS°rxn) using the formula: ΔS°rxn = ΣS°(products) - ΣS°(reactants).

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Key Concepts

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

Standard Entropy (ΔS°)

Standard entropy (ΔS°) is a measure of the disorder or randomness in a system at standard conditions (1 atm, 25°C). It quantifies the amount of energy that is unavailable to do work due to the dispersal of energy among the particles in a substance. Higher entropy values indicate greater disorder, while lower values suggest more order.

Entropy Change in Reactions

The change in entropy (ΔS°rxn) for a chemical reaction is calculated by considering the difference in standard entropies of the products and reactants. It is given by the equation ΔS°rxn = ΣS°(products) - ΣS°(reactants). A positive ΔS°rxn indicates an increase in disorder, while a negative value suggests a decrease in disorder during the reaction.
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Rationalizing the Sign of ΔS°rxn

Rationalizing the sign of ΔS°rxn involves analyzing the physical states and the number of moles of reactants and products. Generally, reactions that produce gases from solids or liquids, or increase the number of gas molecules, tend to have a positive ΔS°rxn. Conversely, reactions that produce fewer gas molecules or convert gases to liquids or solids typically exhibit a negative ΔS°rxn.
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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. b. Cr2O3(s) + 3 CO(g) → 2 Cr(s) + 3 CO2(g)

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Textbook Question

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

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Textbook Question

Rank each set of substances in order of increasing standard molar entropy (S°). Explain your reasoning. a. I2(g); F2(g); Br2(g); Cl2(g) b. H2O(g); H2O2(g); H2S(g) c. C(s, graphite); C(s, diamond); C(s, amorphous)

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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. C(s) + H2O(g) → CO(g) + H2(g)

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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. d. N2O4(g) + 4 H2(g) → N2(g) + 4 H2O(g)

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