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)

Verified step by step guidance

Step 1: Identify the standard enthalpy of formation (ΔH°f), standard entropy (S°), and standard Gibbs free energy of formation (ΔG°f) for each reactant and product from Appendix C.

Step 2: For each reaction, calculate the change in enthalpy (ΔH°) using the formula: ΔH° = Σ(ΔH°f of products) - Σ(ΔH°f of reactants).

Step 3: Calculate the change in entropy (ΔS°) for each reaction using the formula: ΔS° = Σ(S° of products) - Σ(S° of reactants).

Step 4: Calculate the change in Gibbs free energy (ΔG°) for each reaction using the formula: ΔG° = Σ(ΔG°f of products) - Σ(ΔG°f of reactants).

Step 5: Verify the calculations by checking the units and ensuring that the values are consistent with the expected signs for spontaneous reactions (ΔG° < 0).

Key Concepts

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

Enthalpy Change (ΔH°)

Enthalpy change (ΔH°) is the heat content change of a system at constant pressure during a chemical reaction. It indicates whether a reaction is exothermic (releases heat, ΔH° < 0) or endothermic (absorbs heat, ΔH° > 0). This value can be calculated using standard enthalpies of formation from tabulated data, which represent the energy change when one mole of a compound is formed from its elements in their standard states.

Entropy Change (ΔS°)

Entropy change (ΔS°) measures the disorder or randomness in a system during a reaction. A positive ΔS° indicates an increase in disorder, while a negative ΔS° suggests a decrease. Entropy values can be derived from standard molar entropy values, which reflect the amount of energy unavailable for work due to the disorder of the system. Understanding ΔS° is crucial for predicting the spontaneity of reactions.

Gibbs Free Energy Change (ΔG°)

Gibbs free energy change (ΔG°) combines enthalpy and entropy changes to determine the spontaneity of a reaction at constant temperature and pressure. It is calculated using the equation ΔG° = ΔH° - TΔS°, where T is the temperature in Kelvin. A negative ΔG° indicates that a reaction is spontaneous, while a positive ΔG° suggests it is non-spontaneous. This concept is essential for understanding the thermodynamic favorability of chemical processes.

Recommended video:

Guided course

01:51

Gibbs Free Energy of Reactions

Related Practice

Textbook Question

For a certain chemical reaction, ΔH° = -35.4 kJ and ΔS° = -85.5 J/K. (b) Does the reaction lead to an increase or decrease in the randomness or disorder of the system?

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 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)