Question

Calculate the enthalpy of the reaction{\rm 2NO}({\rm g}) + {\rm O_2}({\rm g}) \rightarrow {\rm 2NO_2}({\rm g})given the following reactions and enthalpies of formation: {\rm \frac {_1}{^2} N_2}({\rm g}) + {\rm O_2}({\rm g}) \rightarrow {\rm NO_2}({\rm g}), ~~~\Delta H^{\circ}_{\rm A} = 33.2 \rm ~kJ {\rm \frac {_1}{^2} N_2}({\rm g}) + {\rm \frac {_1}{^2} O_2}({\rm g}) \rightarrow {\rm NO}({\rm g}), ~~\Delta H^{\circ}_{\rm B} = 90.2 \rm ~kJExpress your answer numerically in kilojoules.