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?

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Identify the given entropy change, ΔS°, which is -85.5 J/K.

Understand that entropy, represented by 'S', is a measure of the randomness or disorder of a system.

Recognize that a negative ΔS° indicates a decrease in entropy.

Conclude that if ΔS° is negative, the randomness or disorder of the system decreases during the reaction.

Thus, the reaction leads to a decrease in the randomness or disorder of the system.

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Key Concepts

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

Enthalpy (ΔH)

Enthalpy is a measure of the total energy of a thermodynamic system, often associated with heat transfer during a reaction at constant pressure. A negative ΔH indicates that the reaction is exothermic, meaning it releases heat to the surroundings. This can influence the spontaneity of a reaction, as exothermic reactions tend to favor product formation.

Entropy (ΔS)

Entropy is a measure of the disorder or randomness in a system. A negative ΔS indicates that the reaction leads to a decrease in disorder, meaning the products are more ordered than the reactants. Understanding entropy is crucial for predicting the spontaneity of reactions, as systems tend to evolve towards higher entropy.

Gibbs Free Energy (ΔG)

Gibbs Free Energy combines enthalpy and entropy to determine the spontaneity of a reaction at constant temperature and pressure. The relationship is given by the equation ΔG = ΔH - TΔS. A negative ΔG indicates that a reaction is spontaneous, while a positive ΔG suggests non-spontaneity. In this case, the signs of ΔH and ΔS will help assess the overall spontaneity.

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Gibbs Free Energy of Reactions

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Textbook Question

(a) For a process that occurs at constant temperature, does the change in Gibbs free energy depend on changes in the enthalpy and entropy of the system?

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Textbook Question

(b) For a certain process that occurs at constant T and P, the value of ΔG is positive. Is the process spontaneous?

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)