Calculate the heat of dissociation N2O4 into NO2 from the data :N2+O2→2NO; ΔH=43.10kcal              . . . (1) N2+2O2→N2O4; ΔH=−1.870kcal       . . . .(2)2NO2→2NO+O2;ΔH=+26.10kcal          . . . .(3)

We have to find ΔH for N2O4→2NO2; ΔH=?Add Eqs. (2) and (3)N2+2O2→N2O4; ΔH=−1.87kcal2NO2→2NO+O2; ΔH=26.10kcal∴N2+2O2+2NO2→N2O4+2NO+O2; ΔH=+24.23kcal or N2+O2+2NO2→N2O4+2NO;ΔH=24.23kcalSubtract Eq. (l) from Eq. (4), we getN2+O2⟶2NO;ΔH=+43.10kcalN2+O2⟶2NO2⟶N2O2+2NO;ΔH=24.23kcal--------------------2NO2⟶N2O4;ΔH=−18.87kcal or N2O4→2NO2; ΔH=+18.87kcal i.e., Heat of dissociation of N2O4=+18.87kcal