Question

Comment on the thermodynamic stability of NO_(g), given

\[\ce{1/2 N_2 (g) + 1/2 O2(g) → NO(g)}\]; Δ_rH^θ = 90 kJ mol^–1

\[\ce{NO(g) +1/2 O2(g) → NO2(g)}\] : Δ_rH^θ= –74 kJ mol^–1

Answer 1

The positive value of Δ_rH indicates that heat is absorbed during the formation of NO_(g). This means that NO_(g) has higher energy than the reactants (N₂ and O₂). Hence, NO_(g) is unstable.

The negative value of Δ_rH indicates that heat is evolved during the formation of NO_2(g) from NO_(g)and O_2(g). The product, NO_2(g) is stabilized with minimum energy.

Hence, unstable NO_(g) changes to stable NO_2(g).