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

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Understand the concept of Gibbs Free Energy (ΔG): Gibbs Free Energy is a thermodynamic potential that can be used to predict the spontaneity of a process at constant temperature and pressure.

Recall the spontaneity criterion: A process is spontaneous if the change in Gibbs Free Energy (ΔG) is negative. If ΔG is positive, the process is non-spontaneous under the given conditions.

Analyze the given condition: The problem states that ΔG is positive for the process occurring at constant temperature and pressure.

Apply the spontaneity criterion to the given condition: Since ΔG is positive, according to the criterion, the process is not spontaneous.

Conclude based on the analysis: The process is non-spontaneous at constant temperature and pressure because the value of ΔG is positive.

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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 system at constant temperature and pressure. A negative ΔG indicates that a process can occur spontaneously, while a positive ΔG suggests that the process is non-spontaneous under the given conditions.

Spontaneity of Reactions

The spontaneity of a reaction refers to its ability to proceed without external intervention. A spontaneous process is characterized by a decrease in free energy (ΔG < 0), meaning it can occur naturally. Conversely, if ΔG is positive, the process is not spontaneous and requires energy input to occur.

Thermodynamic Equilibrium

Thermodynamic equilibrium is the state of a system where macroscopic properties are uniform and do not change over time. At equilibrium, the Gibbs Free Energy is at a minimum, and any process that would increase ΔG is not spontaneous. A positive ΔG indicates that the system is not at equilibrium and will not proceed spontaneously in the forward direction.

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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

(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

Using S° values from Appendix C, calculate ΔS° values for the following reactions. In each case, account for the sign of ΔS°.

(a) C₂H₄(g) + H₂(g) → C₂H₆(g)

(b) N₂O₄(g) → 2 NO₂(g)

(d) 2 CH₃OH(g) + 3 O₂(g) ⟶ 2 CO₂(g) + 4 H₂O(g)

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?