Conversion of `SO_2` to `SO_3` is

Options

A. Exothermic reaction
B. Endothermic reaction
C. Photochemical reaction
D. Reduction reaction

Explanation

To determine the nature of the reaction for the conversion of sulfur dioxide (SO₂) to sulfur trioxide (SO₃), we can analyze the reaction step-by-step.

### Step 1: Understand the Reaction
The reaction can be represented as:
\[ 2 \text{SO}_2 (g) + \text{O}_2 (g) \rightarrow 2 \text{SO}_3 (g) \]

### Step 2: Identify the Type of Reaction
We need to classify the reaction based on the heat exchange involved. The options provided are:
- A) Exothermic reaction
- B) Endothermic reaction
- C) Photochemical reaction
- D) Reduction reaction

### Step 3: Analyze the Enthalpy Change
The enthalpy change (ΔH) for the reaction is given as:
\[ \Delta H = -296 \text{ kJ/mol} \]
A negative ΔH indicates that heat is released during the reaction, which is characteristic of an exothermic reaction.

### Step 4: Stability of Products
In this reaction, sulfur in SO₃ has a higher oxidation state (+6) compared to sulfur in SO₂ (+4). The formation of SO₃ from SO₂ involves the release of energy, as the product (SO₃) is more stable than the reactant (SO₂).

### Step 5: Conclusion
Since the reaction releases heat and the products are more stable than the reactants, we conclude that the conversion of SO₂ to SO₃ is an exothermic reaction.

### Final Answer
The correct answer is:
**A) Exothermic reaction**

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