The heat of neutralisation will be highest for which of the following neutralisation reactions?

Options

A. `NH_4OH and HCl`
B. `NH_4OH and CH_3COOH`
C. `NaOH and HCl`
D. `NaOH and CH_3COOH`

Answer

To determine which neutralization reaction has the highest heat of neutralization, we need to analyze the nature of the acids and bases involved in the reactions. The 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.

### Step-by-Step Solution:

1. **Understand the Concept of Heat of Neutralization**:
- The heat of neutralization is the energy change that occurs during the reaction between an acid and a base. It is typically measured in kilojoules per mole (kJ/mol) or kilocalories per mole (kcal/mol).
- For strong acids and strong bases, the heat of neutralization is constant and is approximately -57 kJ/mol or -13.7 kcal/mol. This is because they completely dissociate in solution.

2. **Identify the Types of Acids and Bases**:
- Strong acids (e.g., HCl, HNO3) and strong bases (e.g., NaOH, KOH) fully dissociate in solution.
- Weak acids (e.g., CH3COOH) and weak bases (e.g., NH4OH) do not fully dissociate, resulting in lower heat of neutralization.

3. **Analyze the Given Options**:
- **Option 1**: NH4OH (weak base) + HCl (strong acid)
- **Option 2**: CH3COOH (weak acid) + NaOH (strong base)
- **Option 3**: HCl (strong acid) + NaOH (strong base)
- **Option 4**: CH3COOH (weak acid) + NH4OH (weak base)

4. **Determine the Heat of Neutralization for Each Option**:
- **Option 1**: NH4OH + HCl → This reaction will have a lower heat of neutralization due to the weak base.
- **Option 2**: CH3COOH + NaOH → This reaction will also have a lower heat of neutralization due to the weak acid.
- **Option 3**: HCl + NaOH → This reaction will have the highest heat of neutralization because both are strong, resulting in complete dissociation and maximum energy release.
- **Option 4**: CH3COOH + NH4OH → This reaction will have the lowest heat of neutralization since both reactants are weak.

5. **Conclusion**:
- The highest heat of neutralization occurs in **Option 3: HCl + NaOH**. This is because it involves a strong acid and a strong base, leading to complete ionization and maximum heat release.

### Final Answer:
The heat of neutralization will be highest for the reaction between HCl (strong acid) and NaOH (strong base).