Enthalpy of neutralization of strong acid with strong base is 13.7 kcal. When an unknown acid (1 eq) is neutralizedwith (1 eq.) strong base, the enthalpy change is 10.7 kcal which of the following statements is/are correct regarding unknown acid?

Options

A. Unknown acid is strong acid
B. Unknown acid is weak acid
C. 3.0 kcal heat utilised to dissociate the unknown acid
D. 10.7 kcal heat utilised to dissociate unknown acid

Answer

To solve the problem, we need to analyze the enthalpy changes involved in the neutralization of a strong acid with a strong base and compare it with the neutralization of an unknown acid with the same strong base.

### Step 1: Understand the given data
- The enthalpy of neutralization of a strong acid with a strong base is given as **-13.7 kcal** (the negative sign indicates that heat is released).
- The enthalpy change when an unknown acid is neutralized with a strong base is given as **-10.7 kcal**.

### Step 2: Analyze the enthalpy change
- For a strong acid, the enthalpy change during neutralization is maximum (in this case, -13.7 kcal).
- The unknown acid has a lower enthalpy change (-10.7 kcal), which indicates that less heat is released compared to a strong acid.

### Step 3: Determine the nature of the unknown acid
- Since the enthalpy change for the unknown acid is less negative than that of a strong acid, it suggests that the unknown acid does not completely dissociate into H⁺ ions as a strong acid would. Therefore, the unknown acid must be a **weak acid**.

### Step 4: Calculate the heat utilized to dissociate the unknown acid
- The difference in enthalpy change between the strong acid and the unknown acid can be calculated:
\[ \text{Heat utilized to dissociate the unknown acid} = (-13.7 \text{ kcal}) - (-10.7 \text{ kcal}) = -13.7 + 10.7 = -3 \text{ kcal} \]
- This means that **3 kcal** of energy is utilized to dissociate the unknown acid.

### Step 5: Evaluate the options
1. **Unknown acid is a strong acid** - **Incorrect** (we determined it is a weak acid).
2. **Unknown acid is a weak acid** - **Correct** (as concluded from the analysis).
3. **3 kcal heat utilized to dissociate the unknown acid** - **Correct** (calculated from the difference in enthalpy).
4. **10.7 kcal heat utilized to dissociate unknown acid** - **Incorrect** (the heat utilized is 3 kcal, not 10.7 kcal).

### Conclusion
The correct statements regarding the unknown acid are:
- The unknown acid is a weak acid.
- 3 kcal of heat is utilized to dissociate the unknown acid.