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AP Chemistry Practice Quiz: Free Energy of Dissolution

Written by AP Content Team, Verified for 2026 AP Exams, Last updated: May 2026

Test your understanding with short quizzes. This quiz has 7 questions to check your progress.

Question 1 of 7

The solubility of a salt is a measure of the spontaneity of its dissolution. This spontaneity is determined by the overall change in which thermodynamic property?

All Questions (7)

The solubility of a salt is a measure of the spontaneity of its dissolution. This spontaneity is determined by the overall change in which thermodynamic property?

A) Enthalpy (ΔH°)

B) Entropy (ΔS°)

C) Free Energy (ΔG°)

D) Internal Energy (ΔE°)

Correct Answer: C

The provided content relates the solubility of a salt to the changes in enthalpy and entropy, which combine to determine the free energy change (ΔG°). A spontaneous process, like dissolution, is characterized by a negative ΔG°.

According to the provided information, why is it challenging to predict the total free energy change (ΔG°) for the dissolution of a salt?

A) Because the entropy change is always negligible.

B) Because the process is always highly endothermic.

C) Because the temperature of the solvent cannot be controlled.

D) Because of potential cancellations among competing energy factors.

Correct Answer: D

The content explicitly states that predicting the total ΔG° can be challenging due to cancellations among the multiple factors involved, such as the energy required to break the solid's interactions and the energy released from the interaction of the dissolved species with the solvent.

The overall dissolution process involves several steps. Which of the following is described as a key factor contributing to the total free energy change?

A) The change in atmospheric pressure.

B) The interaction of the dissolved species with the solvent.

C) The final concentration of the solution.

D) The rate at which the salt dissolves.

Correct Answer: B

The provided text lists three factors that contribute to the free energy change of dissolution: breaking the solid's interactions, reorganizing the solvent, and the interaction of the dissolved species with the solvent.

A salt is observed to dissolve spontaneously in water, even though the process is endothermic (ΔH° > 0). Based on the relationship between free energy, enthalpy, and entropy, what must be true for this to occur?

A) The change in entropy (ΔS°) must be negative.

B) The change in entropy (ΔS°) must be positive and significant.

C) The free energy change (ΔG°) must be positive.

D) The interactions within the solid must be very weak.

Correct Answer: B

For a process to be spontaneous, ΔG° must be negative. The relationship is ΔG° = ΔH° - TΔS°. If ΔH° is positive (endothermic), the only way for ΔG° to be negative is if the TΔS° term is positive and larger in magnitude. This requires a significant positive change in entropy (ΔS°).

Which step in the dissolution process inherently requires an input of energy to overcome attractive forces?

A) The interaction of the dissolved species with the solvent.

B) The increase in the overall disorder of the system.

C) The reorganization of the solvent around the dissolved species.

D) The breaking of the solid's interactions.

Correct Answer: D

The content identifies "breaking the solid's interactions" as a key factor. This step, also known as overcoming the lattice energy, requires energy input to separate the constituent particles of the solid and is therefore an endothermic contribution to the overall enthalpy change.

The solubility of a salt is fundamentally linked to the changes in which two thermodynamic quantities during the dissolution process?

A) Pressure and Volume

B) Enthalpy and Entropy

C) Temperature and Molarity

D) Activation Energy and Reaction Rate

Correct Answer: B

The provided content directly states the relationship between the solubility of a salt and the changes in enthalpy (ΔH) and entropy (ΔS) that occur during dissolution.

The total free energy change for dissolution is a net result of several contributing factors. Which factor is generally an energy-releasing (exothermic) process that favors dissolution?

A) Breaking the interactions within the solid lattice.

B) Breaking the interactions between solvent molecules.

C) The interaction of dissolved species with the solvent.

D) A decrease in the entropy of the system.

Correct Answer: C

The content identifies the "interaction of the dissolved species with the solvent" as a key factor. This step, known as solvation or hydration, involves the formation of new, stable interactions and typically releases energy, making it an exothermic contribution that helps drive the dissolution process.