Which of the following reactions is defines `Delta_(f)H^(Theta)`?

Options

A. `C("diamond") +O_(2)(g) rarr CO_(2)(g)`
B. `(1)/(2)H_(2)(g) +(1)/(2)F_(2)(g) rarr HF (g)`
C. `N_(2)(s) +3H_(2)(g) rarr 2NH_(3)(g)`
D. `CO(g) +(1)/(2)O_(2)(g) rarr CO_(2)(g)`

Explanation

To determine which of the given reactions defines the standard enthalpy of formation (Δ_fH^Θ), we need to understand the definition of the standard enthalpy of formation. It is defined as the amount of heat evolved or absorbed when one mole of a compound is formed from its constituent elements in their standard states.

### Step-by-Step Solution:

1. **Understand the Definition**: The standard enthalpy of formation (Δ_fH^Θ) is the heat change when one mole of a compound is formed from its elements in their standard states.

2. **Analyze Each Reaction**:
- **Option A**: C (diamond) → This does not represent a reaction forming a compound from its elements, as diamond is a form of carbon and does not react to form a compound.
...