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

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

Note that we need to multiply each ΔH˚_{f} by the stoichiometric coefficient since ΔH˚_{f} is in kJ/mol.

Also, note that ΔH˚f for elements in their standard state is 0.

**Reaction: **C_{2}H_{4}(g) + O_{3}(g) → CH_{3}CHO(g) + O_{2}(g)

**Given:**

**Element/ Compound** **Standard Heat of Formation (kJ/mol)**

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

(c) C_{2}H_{4}(g) + O_{3}(g) → CH_{3}CHO(g) + O_{2}(g)

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