We can use the following equation to solve for **ΔH˚ _{rxn}**:

$\overline{){\mathbf{\Delta H}}{{\mathbf{\xb0}}}_{{\mathbf{rxn}}}{\mathbf{=}}{\mathbf{\Delta H}}{{\mathbf{\xb0}}}_{\mathbf{f}\mathbf{,}\mathbf{}\mathbf{prod}}{\mathbf{-}}{\mathbf{\Delta H}}{{\mathbf{\xb0}}}_{\mathbf{f}\mathbf{,}\mathbf{}\mathbf{react}}}$

Use **ΔH˚ _{f} **from textbook/online

Note that we need to *multiply each ΔH˚ _{f} by the stoichiometric coefficient* since ΔH˚

Calculate ΔH° for each of the following reactions, which occur in the atmosphere.

(a) C2H4(g) + O3(g) → CH3CHO(g) + O2(g)

(b) O3(g) + O(g) → 2 O2(g)