Which of the following indicates the heat of reaction equal to heat of formation?

Options

A. `C("graphite") + O_(2)(1 atm) rarr CO_(2)(1 atm)`
B. `C("diamond") + O_(2)(1 atm) rarr CO_(2)(2 atm)`
C. `C("graphite") + O_(2)(1 atm) rarr CO_(2)(2 atm)`
D. `C("diamond") + O_(2)(1 atm) rarr CO_(2)(1 atm)`

Explanation

To determine which option indicates that the heat of reaction is equal to the heat of formation, we need to understand the definition of heat of formation (ΔHf). The heat of formation is defined as the enthalpy change when one mole of a compound is formed from its constituent elements in their standard states under standard conditions (298 K and 1 atm pressure).

### Step-by-Step Solution:

1. **Understand the Definition of Heat of Formation (ΔHf)**:
- ΔHf is the enthalpy change when one mole of a substance is formed from its elements in their standard states at 298 K and 1 atm pressure.

2. **Analyze Each Option**:
- **Option 1**: Formation of 1 mole of CO2 from graphite (C) and O2 under standard conditions (1 atm and 298 K).
- Reaction: C (s, graphite) + O2 (g) → CO2 (g)
- This reaction meets the criteria for ΔHf, as it involves the formation of 1 mole of CO2 from its elements in their standard states.
- **Conclusion**: This option is correct.

- **Option 2**: Formation of 1 mole of CO2 from carbon in diamond form and O2 at 280 m pressure.
- Reaction: C (diamond) + O2 (g) → CO2 (g)
- This option is incorrect because diamond is not the standard state of carbon, and the pressure is not standard (1 atm).

- **Option 3**: Formation of 1 mole of CO2 from graphite and O2 at 2 atm pressure.
- Reaction: C (s, graphite) + O2 (g) → CO2 (g)
- This option is incorrect because, although carbon is in its standard state, the pressure is not standard (1 atm).

- **Option 4**: Formation of 1 mole of CO2 from carbon in diamond form and O2 at 1 atm.
- Reaction: C (diamond) + O2 (g) → CO2 (g)
- This option is incorrect because diamond is not the standard state of carbon.

3. **Final Conclusion**:
- Only **Option 1** indicates that the heat of reaction is equal to the heat of formation, as it satisfies all the conditions for ΔHf.

### Summary:
The correct answer is **Option 1**.