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Ch.19 - Chemical Thermodynamics
All textbooksBrown 14th EditionCh.19 - Chemical ThermodynamicsProblem 59
Chapter 19, Problem 59

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)
(b) NO2(g) + N2O(g) → 3 NO(g)
(c) 6 Cl2(g) + 2 Fe2O3(s) → 4 FeCl3(s) + 3 O2(g)
(d) SO2(g) + 2 H2(g) → S(s) + 2 H2O(g)

Verified step by step guidance
1
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.
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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.
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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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Related Practice
Textbook Question

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

a. 4 Cr(s) + 3 O2(g) → 2 Cr2O3(s)

b. BaCO3(s) → BaO(s) + CO2(g)

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

d. K(s) + O2(g) → KO2(s)

Textbook Question

Using data from Appendix C, calculate the change in Gibbs free energy for each of the following reactions. In each case, indicate whether the reaction is spontaneous at 298 K under standard conditions.

(a) 2 Ag(s) + Cl2(g) → 2 AgCl(s)

(b) P4O10(s) + 16 H2(g) → 4 PH3(g) + 10 H2O(g)

(c) CH4(g) + 4 F2(g) → CF4(g) + 4 HF(g)

(d) 2 H2O2(l) → 2 H2O(l) + O2(g)