When a strong acid, strong base or their salt are dissolved in water, they are completely ionised. If a strong acid is added to a strong base, `H^(+)` ions from the former combine with `OH^(-)` ions of the latter forming water. The formation of each water molecule liberates a certain quantity of energy and the reaction is exothermic. The heat liberated when one mole of water is formed by combining hydrochloric acid sodium hydroxide is 13.7 kcal. The heat liberated when one mole of water is formed by combining sulphuic acid and sodium hydroxide is

Options

A. 25.5 kcal
B. 8.5 kcal
C. 13.7 kcal
D. 34 kcal

Answer

To solve the problem, we need to analyze the reaction between sulfuric acid (H₂SO₄) and sodium hydroxide (NaOH) and determine the heat liberated when one mole of water is formed.

### Step-by-Step Solution:

1. **Write the Reaction**:
The reaction between sulfuric acid and sodium hydroxide can be written as:
\[ H_2SO_4 + 2NaOH \rightarrow Na_2SO_4 + 2H_2O \]
This shows that one mole of sulfuric acid reacts with two moles of sodium hydroxide to produce one mole of sodium sulfate and two moles of water.

**Hint**: Always start by writing the balanced chemical equation for the reaction.

2. **Identify the Heat of Reaction**:
We know from the problem that when hydrochloric acid (HCl) reacts with sodium hydroxide (NaOH), the heat liberated is 13.7 kcal for the formation of one mole of water.

**Hint**: Recognize that the heat released in the neutralization reaction between a strong acid and a strong base is a characteristic value.

3. **Relate the Reactions**:
The reaction of sulfuric acid with sodium hydroxide is similar to that of hydrochloric acid with sodium hydroxide in terms of the neutralization process. The formation of water from H⁺ and OH⁻ ions releases energy.

**Hint**: Understand that the energy change associated with the formation of water is similar for strong acids and strong bases.

4. **Determine the Heat Released for Sulfuric Acid**:
Since the reaction of sulfuric acid with sodium hydroxide also involves the formation of water, we can conclude that the heat released for the formation of one mole of water in this reaction is also 13.7 kcal.

**Hint**: If the reaction is similar, the heat released will be the same unless stated otherwise.

5. **Final Answer**:
Therefore, the heat liberated when one mole of water is formed by combining sulfuric acid and sodium hydroxide is:
\[ \text{Heat liberated} = 13.7 \text{ kcal} \]

### Conclusion:
The heat liberated when one mole of water is formed by combining sulfuric acid and sodium hydroxide is **13.7 kcal**.

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