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

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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Related Practice

Textbook Question

For a certain chemical reaction, ΔH° = -35.4 kJ and ΔS° = -85.5 J/K. (c) Calculate ΔG° for the reaction at 298 K. (d) Is the reaction spontaneous at 298 K under standard conditions?

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)

(d) 2 H₂O₂(l) → 2 H₂O(l) + O₂(g)

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°.