Question

Using the ΔHf data provided, calculate ΔH in kJ mol-1 for the following reaction: 

2NO2(g) ⇋ N2O4(g)

Answer 1

$\Delta$ H_r = $\Sigma\Delta$ H_f(product) - $\Sigma\Delta$ H_f(reagent);

We don't know the ΔH_f data provided;

Therefore,

$\Delta$ H_r = $\Delta$ H_f(N₂O₄) - 2 * $\Delta$ H_f(NO₂).