Which of the following does not represent heat of formation `(Delta H_f^@)` ?

Options

A. `C_("graphite") + O_(2)(g) to CO_(2)(g)`
B. `H_(2)(g) + 1/2O_(2)(g) to H_(2)O(l)`
C. `2CO(g) + O_(2)(g) to 2CO_(2)(g)`
D. All of these

Explanation

To solve the question of which option does not represent the heat of formation (ΔH_f^@), we need to understand the definition of heat of formation. The heat of formation is defined as the heat change that occurs when one mole of a compound is formed from its constituent elements in their standard states.

### Step-by-Step Solution:

1. **Understand the Definition**:
- Heat of formation (ΔH_f^@) is the heat change when one mole of a compound is formed from its elements in their standard states.

2. **Analyze Each Option**:
- **Option 1**: Formation of 1 mole of CO2 from its elements (C in graphite and O2 gas).
- This represents heat of formation because it forms one mole of CO2 from its elements in their standard states.

- **Option 2**: Formation of 1 mole of H2O from its elements (H2 gas and O2 gas).
- This also represents heat of formation as it forms one mole of H2O from its elements in their standard states.

- **Option 3**: Formation of 2 moles of CO2 from its elements.
- This does NOT represent heat of formation because it does not form one mole of the compound; it forms two moles instead.

3. **Conclusion**:
- The option that does not represent heat of formation is **Option 3**.

### Final Answer:
**Option 3** does not represent heat of formation (ΔH_f^@).

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