Contact process is used to convert `SO_2` into `SO_3` , in the pres ence of platinum catalyst and the reaction is exothermic.
`2SO_2(g)+O_2(g) Leftrightarrow 2SO_3(g)DeltaH=(-)ve`
During the conversion of `SO_3` into `H_2SO_4` on commer- cial scale, the intermediate compound is

Options

A. `H_2S_2O_3`
B. `H_2S_2O_5`
C. `H_2S_2O_6`
D. `H_2S_2O_7`

Answer

To solve the question about the intermediate compound formed during the conversion of \( SO_3 \) into \( H_2SO_4 \) in the Contact Process, we can follow these steps:

### Step 1: Understand the Contact Process
The Contact Process is a method used to produce sulfuric acid (\( H_2SO_4 \)) from sulfur dioxide (\( SO_2 \)). The first step involves the conversion of \( SO_2 \) to sulfur trioxide (\( SO_3 \)) in the presence of a platinum catalyst. The reaction is exothermic:

\[ 2SO_2(g) + O_2(g) \leftrightarrow 2SO_3(g) \quad \Delta H < 0 \]

### Step 2: Identify the Next Step
Once \( SO_3 \) is produced, it is then converted into sulfuric acid (\( H_2SO_4 \)). However, this conversion does not happen directly. Instead, \( SO_3 \) first reacts with water to form \( H_2SO_4 \).

### Step 3: Determine the Intermediate Compound
Before \( SO_3 \) can react with water to form \( H_2SO_4 \), it can form an intermediate compound known as oleum, which has the chemical formula \( H_2S_2O_7 \). This compound can be represented as:

\[ SO_3 + H_2O \rightarrow H_2S_2O_7 \quad (\text{Olium}) \]

### Step 4: Final Conversion to Sulfuric Acid
The oleum can then react with water to produce sulfuric acid:

\[ H_2S_2O_7 + H_2O \rightarrow 2H_2SO_4 \]

### Conclusion
Thus, the intermediate compound formed during the conversion of \( SO_3 \) into \( H_2SO_4 \) is \( H_2S_2O_7 \), commonly known as oleum.

### Final Answer
The intermediate compound is \( H_2S_2O_7 \) (Olium).

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