What is the standard heat of reaction for the formation of NO2 (g) from NO (g) and O2 (g) ? Write the balanced equation first.

- 113.10 kJ/mol.

Explanation:

Firstly, we should write the balanced equation of NO₂ formation.

2NO + O₂ → 2NO₂.

We have the standard heat of formation (ΔH°f) of:

ΔH°f for NO = 90.4 kJ/mol.

ΔH°f for O₂ = 0.0 kJ/mol. (element)

ΔH°f for NO₂ = 33.85 kJ/mol.

∵ ΔH° for the reaction = ∑ (ΔH°f) products - ∑ (ΔH°f) reactants = [2 (33.85 kJ/mol) ] - [1 (0.0 kJ/mol) + 2 (90.4 kJ/mol) ] = 67.7 kJ/mol - 180.8 kJ/mol = - 113.10 kJ/mol.