Sulfur dioxide reacts with strontium oxide as follows: SO2(g) + SrO(g) → SrSO3(s). (b) If you had only standard enthalpy data for this reaction, how would you estimate the value of ΔG° at 298 K, using data from Appendix C on other substances?

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Identify the standard enthalpy change (ΔH°) for the reaction using the enthalpy data from Appendix C for each substance involved in the reaction. Calculate ΔH° using the formula: ΔH° = ΣΔH°(products) - ΣΔH°(reactants).

Determine the standard entropy change (ΔS°) for the reaction using the entropy data from Appendix C for each substance. Calculate ΔS° using the formula: ΔS° = ΣS°(products) - ΣS°(reactants).

Use the Gibbs free energy equation to estimate ΔG° at 298 K: ΔG° = ΔH° - TΔS°, where T is the temperature in Kelvin (298 K in this case).

Ensure that the units are consistent when performing the calculation. Typically, ΔH° is in kJ/mol and ΔS° is in J/mol·K, so you may need to convert ΔS° to kJ/mol·K by dividing by 1000.

Interpret the sign and magnitude of ΔG° to understand the spontaneity of the reaction at 298 K. A negative ΔG° indicates a spontaneous reaction under standard conditions.

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 system at constant temperature and pressure. It is a crucial concept in predicting the spontaneity of a reaction; a negative ΔG° indicates a spontaneous process, while a positive value suggests non-spontaneity. The relationship between ΔG°, enthalpy (ΔH°), and entropy (ΔS°) is given by the equation ΔG° = ΔH° - TΔS°, where T is the temperature in Kelvin.

Standard Enthalpy of Formation (ΔH°f)

The standard enthalpy of formation (ΔH°f) is the change in enthalpy when one mole of a compound is formed from its elements in their standard states. This value is essential for calculating the overall enthalpy change (ΔH°) for a reaction using Hess's law, which states that the total enthalpy change for a reaction is the sum of the enthalpy changes for individual steps. By knowing the ΔH°f values of the reactants and products, one can determine ΔH° for the reaction.

Entropy (ΔS°)

Entropy (ΔS°) is a measure of the disorder or randomness in a system. In chemical reactions, changes in entropy can significantly influence the spontaneity of the process. A positive ΔS° indicates an increase in disorder, which can favor spontaneity, especially at higher temperatures. To estimate ΔG° at 298 K, one must consider both the enthalpy and entropy changes, as they collectively determine the Gibbs Free Energy of the reaction.

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Related Practice

Textbook Question

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)

(d) SO₂(g) + 2 H₂(g) → S(s) + 2 H₂O(g)

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°.

Textbook Question

Classify each of the following reactions as one of the four possible types summarized in Table 19.3: (i) spontanous 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.

(a) N₂(g) + 3 F₂(g) → 2 NF₃₍g) ΔH° = -249 kJ; ΔS° = -278 J/K

(b) N₂(g) + 3 Cl₂(g) → 2 NCl₃(g) ΔH° = 460 kJ; ΔS° = -275 J/K

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.