Question

Which of the following indicates an exothermic heat of solution? A. Heat is evolved. B. The final solution is acidic. C. A precipitate is formed. D. The reaction is spontaneous.

Short answer

A. Heat is evolved.

Step-by-step solution

Understand the Question

Identify what is being asked. The question is asking which statement indicates an exothermic heat of solution.

Recall the Definition

An exothermic process releases heat to the surroundings. This is a key characteristic to keep in mind.

Analyze the Options

Let's go through each option: A. Heat is evolved: This directly indicates that heat is released, which matches our definition of an exothermic process. B. The final solution is acidic: This characteristic does not necessarily indicate anything about heat release. C. A precipitate is formed: Formation of a precipitate does not necessarily involve release of heat. D. The reaction is spontaneous: Spontaneity does not indicate whether heat is absorbed or released.

Choose the Correct Option

Based on our analysis, the correct option is A. Heat is evolved.

Key concepts

heat of solution

The 'heat of solution' refers to the heat exchanged when a solute dissolves in a solvent. This can either be absorbed or released as the process takes place. Two main types of heat changes occur during dissolution:

• Endothermic: Absorbs heat, making the surroundings cooler.
• Exothermic: Releases heat, warming the surroundings.

In our exercise, we focus on the exothermic type. An exothermic heat of solution occurs when the interactions between solute and solvent release more energy than is used to break up the solute and solvent molecules.

exothermic reaction

An exothermic reaction is a type of chemical reaction that releases energy, typically in the form of heat, to its surroundings. This happens because the total energy of the products is less than that of the reactants. Common indicators are:

• Temperature of the surroundings increases.
• Heat is evolved or given off during the reaction.

In our specific case, the reaction involves the dissolution of a substance in a solvent where heat is released. As correctly identified in the exercise by option A, 'Heat is evolved,' indicates an exothermic process. The other options do not necessarily relate to heat being released.

energy release

Energy release in the context of chemical reactions and solutions typically involves the transfer of heat. In exothermic processes, energy is released because the bond formation in the solution phase releases more energy than is required to break the bonds in the solute and solvent. This released energy manifests as heat, making it an exothermic reaction.
For a clear understanding:

• Initial energy required to break solute and solvent bonds: Input.
• Energy released upon formulating new bonds: Output.

If the output energy is greater than the input energy, heat is released. This substantial energy release aligns with the answer to our exercise, making it clear why option A is correct.