Question

if the bond enthalpy of o₂(g) is 492 kj/mol, calculate δh°f for o(g). round your answer to 3 significant digits. note: reference the thermodynamic properties of pure substances table for additional information.

Explanation:

Step1: Relate bond enthalpy to reaction enthalpy

The bond enthalpy of $\text{O}_2(g)$ is the energy to break 1 mol of $\text{O=O}$ bonds: $\text{O}_2(g)
ightarrow 2\text{O}(g)$, so $\Delta H = 492\ \text{kJ/mol}$.

Step2: Calculate $\Delta H_f^\circ$ for $\text{O}(g)$

$\Delta H_f^\circ$ is the enthalpy of forming 1 mol of $\text{O}(g)$ from its element (O₂). The reaction is $\frac{1}{2}\text{O}_2(g)
ightarrow \text{O}(g)$, so $\Delta H_f^\circ = \frac{492}{2}\ \text{kJ/mol}$.

Answer:

246