Question

To calculate the enthalpy of the reaction, N2 (g) + 3H2 (g) → 2NH3 (g), you need to subtract which heats of formation?

N2 (g) and H2 (g)

NH3 (g)

N2 (g), H2 (g), and NH3(g)

none of them

Answer 1

When calculating the change in enthalpy of the reaction \(\sf (ΔH_{rxn})\), you subtract the enthalpy of formation of the reactants from the products.

\(\sf ΔH_{rxn}=H_f(products)−H_f(reactants)\)