Question

calculate the standard enthalpy of formation for diamond, given that
round your answer to 2 significant digits.

Explanation:

Step1: Define target reaction

The standard enthalpy of formation for diamond is the enthalpy change of:

$$\text{C(graphite)} ightarrow \text{C(diamond)}$$

Step2: Combine given reactions

Reverse the second reaction:

$$\text{CO}_2(g) ightarrow \text{C(diamond)} + \text{O}_2(g) \quad \Delta H^\circ = +395.3 \, \frac{\text{kJ}}{\text{mol}}$$

Add to the first reaction:

$$\text{C(graphite)} + \text{O}_2(g) + \text{CO}_2(g) ightarrow \text{CO}_2(g) + \text{C(diamond)} + \text{O}_2(g)$$

Step3: Calculate ΔH°

Cancel common species and sum enthalpies:
$$\Delta H^\circ = (-393.4 + 395.3) \, \frac{\text{kJ}}{\text{mol}} = 1.9 \, \frac{\text{kJ}}{\text{mol}}$$

Answer:

1.9 $\frac{\text{kJ}}{\text{mol}}$