Ch.19 - Chemical Thermodynamics

Problem 59a

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Chapter 19, Problem 59a

Using data from Appendix C, calculate ΔG° for the following reactions. Indicate whether each reaction is spontaneous at 298 K under standard conditions. (a) 2 SO₂(g) + O₂(g) → 2 SO₃(g)

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First, identify the standard Gibbs free energy of formation (ΔG°f) values for each reactant and product from Appendix C. You will need the values for SO2(g), O2(g), and SO3(g).

Write the balanced chemical equation: 2 SO2(g) + O2(g) → 2 SO3(g).

Apply the formula for calculating the standard Gibbs free energy change (ΔG°) for the reaction: ΔG° = ΣΔG°f(products) - ΣΔG°f(reactants). Remember to multiply the ΔG°f values by their respective stoichiometric coefficients in the balanced equation.

Substitute the ΔG°f values into the equation and perform the calculation to find ΔG° for the reaction.

Determine if the reaction is spontaneous at 298 K under standard conditions by checking the sign of ΔG°. If ΔG° is negative, the reaction is spontaneous; if positive, it is non-spontaneous.

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Key Concepts

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

Gibbs Free Energy (ΔG°)

Gibbs Free Energy (ΔG°) is a thermodynamic potential that measures the maximum reversible work obtainable from a thermodynamic process at constant temperature and pressure. It is a crucial indicator of spontaneity; if ΔG° is negative, the reaction is spontaneous under standard conditions, while a positive ΔG° indicates non-spontaneity.

Standard Conditions

Standard conditions refer to a set of specific conditions used to measure and compare thermodynamic properties, typically defined as 1 bar of pressure and a specified temperature, usually 298 K (25°C). These conditions allow for consistent calculations of thermodynamic values, such as ΔG°, across different reactions.

Reaction Quotient (Q) and Equilibrium Constant (K)

The reaction quotient (Q) is a measure of the relative concentrations of products and reactants at any point in a reaction, while the equilibrium constant (K) is the value of Q at equilibrium. Comparing Q to K helps determine the direction of the reaction and its spontaneity; if Q < K, the reaction proceeds forward, indicating spontaneity.

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Reaction Quotient Q

Related Practice

A certain reaction has ΔH° = +23.7 kJ and ΔS° = +52.4 J>K. (c) Calculate ΔG° for the reaction at 298 K. (d) Is the reaction spontaneous at 298 K under standard conditions?

Open Question

Using data in Appendix C, calculate ΔH°, ΔS°, and ΔG° at 298 K for each of the following reactions. (a) H₂(g) + F₂(g) → 2 HF(g) (b) C(s, graphite) + 2 Cl₂(g) → CCl₄(g) (c) 2 PCl₃(g) + O₂(g) → 2 POCl₃(g) (d) 2 CH₃OH(g) + H₂(g) → C₂H₆(g) + 2 H₂O(g)

Textbook Question

Use data in Appendix C to calculate ΔH°, ΔS°, and ΔG° at 25 °C for each of the following reactions.

c. 2 P(s) + 10 HF(g) → 2 PF₅(g) + 5 H₂(g)

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Open Question

Without using thermochemical data, predict whether ΔG° for the reaction involving octane (1C8H182) is more negative or less negative than ΔH°.

Textbook Question

Sulfur dioxide reacts with strontium oxide as follows: SO₂(g) + SrO(g) → SrSO₃(s) (a) Without using thermochemical data, predict whether ΔG° for this reaction is more negative or less negative than ΔH°.

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Textbook Question

Classify each of the following reactions as one of the four possible types summarized in Table 19.3: (i) spontaneous at all temperatures; (ii) not spontaneous at any temperature; (iii) spontaneous at low T but not spontaneous at high T; (iv) spontaneous at high T but not spontaneous at low T. (c) N₂F₄(g) ⟶ 2 NF₂(g) ΔH° = 85 kJ; ΔS° = 198 J/K

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Using data from Appendix C, calculate ΔG° for the following reactions. Indicate whether each reaction is spontaneous at 298 K under standard conditions. (a) 2 SO2(g) + O2(g) → 2 SO3(g)

Verified Solution

Key Concepts

Gibbs Free Energy (ΔG°)

Standard Conditions

Reaction Quotient (Q) and Equilibrium Constant (K)

Using data from Appendix C, calculate ΔG° for the following reactions. Indicate whether each reaction is spontaneous at 298 K under standard conditions. (a) 2 SO₂(g) + O₂(g) → 2 SO₃(g)