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 of the given reactions indicates that the heat of reaction is equal to the heat of formation, we will follow these steps:

### Step 1: Understand the Concept of Heat of Formation
The heat of formation (ΔH_f) is defined as the amount of heat released or absorbed when one mole of a compound is formed from its elements in their standard states. For example, the formation of carbon dioxide (CO2) from its elements would be represented as:
\[ \text{C (s, graphite)} + \text{O}_2 \text{(g)} \rightarrow \text{CO}_2 \text{(g)} \]

### Step 2: Analyze the Given Reactions
We are given four reactions, and we need to identify which one corresponds to the heat of formation. The key points to consider are:
- The reaction must produce one mole of the compound.
- The reactants must be in their standard states.

### Step 3: Evaluate Each Reaction
1. **Reaction A**: Check if it produces one mole of the compound from its elements in standard states.
2. **Reaction B**: Check if it uses diamond as carbon instead of graphite.
3. **Reaction C**: Check the pressures of the gases involved.
4. **Reaction D**: Similar to B, check if it uses diamond.

### Step 4: Identify the Correct Reaction
- If Reaction A shows the formation of one mole of a substance from its elements in their standard states (with appropriate pressures), then it is likely the correct answer.
- Reactions B and D can be ruled out if they use diamond as the form of carbon since the standard state of carbon is graphite.
- For Reaction C, ensure that the pressures of the gases are consistent with the standard state.

### Step 5: Conclusion
After evaluating the reactions based on the criteria for heat of formation, the reaction that meets all these conditions is the answer.

### Final Answer
The correct option is **Reaction A**.

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