Heat of neutralization of an acid by a base is highest when

Options

A. Both the acid and base are weak
B. Both the acid and base are strong
C. The acid is strong and the base is weak
D. The acid is weak and the base is strong

Explanation

To determine when the heat of neutralization of an acid by a base is highest, we need to analyze the nature of the acid and base involved in the reaction.

### Step-by-Step Solution:

1. **Understanding Heat of Neutralization**:
- Heat of neutralization is defined as the amount of heat released when one equivalent of an acid reacts with one equivalent of a base to form water and a salt.

2. **Identifying Strong and Weak Acids/Bases**:
- Strong acids (like HCl, HNO3) completely dissociate in water to release H⁺ ions.
- Strong bases (like NaOH, KOH) completely dissociate to release OH⁻ ions.
- Weak acids (like CH₃COOH) and weak bases (like NH₄OH) do not completely dissociate in solution.

3. **Heat Released During Neutralization**:
- When a strong acid reacts with a strong base, the reaction goes to completion, leading to maximum heat release.
- The standard heat of neutralization for strong acid-strong base reactions is approximately 57.2 kJ (or 13.7 kcal).

4. **Effect of Weak Acids and Bases**:
- If either the acid or the base is weak, some energy is required for the ionization of the weak component. This results in less heat being released compared to a strong acid-strong base reaction.

5. **Conclusion**:
- Therefore, the heat of neutralization is highest when both the acid and the base are strong.

### Final Answer:
The heat of neutralization of an acid by a base is highest when both the acid and the base are strong.