The heat of neutralization of NaOH with HCl is 57.3 KJ and with HCN is 12.1 KJ. The heat of ionization of HCN is

Options

A. `+69.4 ` KJ
B. `+45.2` KJ
C. `-45.2` KJ
D. `-69.4` KJ

Answer

To solve the problem of finding the heat of ionization of HCN, we can use the information provided about the heat of neutralization of NaOH with HCl and HCN.

### Step-by-Step Solution:

1. **Understanding the Heat of Neutralization**:
- The heat of neutralization for the reaction between a strong acid (HCl) and a strong base (NaOH) is given as 57.3 kJ. This value represents the energy change when one mole of water is formed from the neutralization of the acid and base.

2. **Heat of Neutralization with Weak Acid**:
- The heat of neutralization for the reaction between NaOH and the weak acid HCN is given as 12.1 kJ. This value is lower than that of the strong acid because the weak acid does not completely ionize in solution.

3. **Setting Up the Equation**:
- The heat of neutralization for a weak acid and strong base can be expressed as:
\[ \Delta H_{\text{neutralization (weak acid)}} = \Delta H_{\text{neutralization (strong acid)}} - \Delta H_{\text{ionization (weak acid)}} \]
- Plugging in the values we have:
\[ 12.1 \, \text{kJ} = 57.3 \, \text{kJ} - \Delta H_{\text{ionization (HCN)}} \]

4. **Rearranging the Equation**:
- To find the heat of ionization of HCN, we rearrange the equation:
\[ \Delta H_{\text{ionization (HCN)}} = 57.3 \, \text{kJ} - 12.1 \, \text{kJ} \]

5. **Calculating the Heat of Ionization**:
- Now, we perform the subtraction:
\[ \Delta H_{\text{ionization (HCN)}} = 57.3 \, \text{kJ} - 12.1 \, \text{kJ} = 45.2 \, \text{kJ} \]

6. **Conclusion**:
- The heat of ionization of HCN is 45.2 kJ.

### Final Answer:
The heat of ionization of HCN is **45.2 kJ**.