Which of the following equations respresents standard heat of formation of `CH_(4)` ?

Options

A. `C_("diamond") + 2H_(2) (g) rightarrow CH_(4)(g)`
B. `C_("graphite") + 2H_(2) (g) rightarrow CH_(4)(g)`
C. `C_("diamond") + 4H(g) rightarrow CH_(4)(g)`
D. `C_("graphite") + 4H(g) rightarrow CH_(4)(g)`

Answer

To determine which equation represents the standard heat of formation of methane (CH₄), we need to understand the definition of standard heat of formation. The standard heat of formation is defined as the heat change when one mole of a substance is formed from its elements in their standard states.

### Step-by-Step Solution:

1. **Identify the Elements of CH₄**:
- The elements that make up methane are carbon (C) and hydrogen (H).

2. **Determine the Standard States of the Elements**:
- The standard state of carbon is graphite, which is the most stable form at 298 K and 1 bar pressure.
- The standard state of hydrogen is diatomic hydrogen gas (H₂).

3. **Write the Formation Reaction**:
- The formation of one mole of methane from its elements in their standard states can be represented as:
\[ \text{C (graphite)} + 2 \text{H}_2 (g) \rightarrow \text{CH}_4 (g) \]

4. **Check the Options**:
- We need to look for an equation that matches the formation reaction we just wrote. The correct equation should include one mole of CH₄ produced from one mole of carbon in its standard state (graphite) and two moles of hydrogen gas.

5. **Conclusion**:
- The correct representation of the standard heat of formation of CH₄ is:
\[ \text{C (graphite)} + 2 \text{H}_2 (g) \rightarrow \text{CH}_4 (g) \]