Which expression correctly gives the standard enthalpy change for the reaction in…

CHEMISTRY · Single correct · A Level · Chemistry · Energetics · Energetics

Problem

Which expression correctly gives the standard enthalpy change ΔHrxn∘\Delta H^{\circ}_{\text{rxn}} for the reaction 2 NO(g)+O2(g)→2 NO2(g)2\,\text{NO}(g)+\text{O}_2(g)\rightarrow 2\,\text{NO}_2(g) in terms of the standard enthalpies of formation ΔHf∘\Delta H^{\circ}_f of the species involved? (a) 2 ΔHf∘(NO)+ΔHf∘(O2)−2 ΔHf∘(NO2)2\,\Delta H^{\circ}_f(\text{NO})+\Delta H^{\circ}_f(\text{O}_2)-2\,\Delta H^{\circ}_f(\text{NO}_2) (b) 2 ΔHf∘(NO2)−2 ΔHf∘(NO)2\,\Delta H^{\circ}_f(\text{NO}_2)-2\,\Delta H^{\circ}_f(\text{NO}) (c) 2 ΔHf∘(NO2)−[2 ΔHf∘(NO)+ΔHf∘(O2)]2\,\Delta H^{\circ}_f(\text{NO}_2)-\left[2\,\Delta H^{\circ}_f(\text{NO})+\Delta H^{\circ}_f(\text{O}_2)\right] (d) ΔHf∘(NO2)−[ΔHf∘(NO)+ΔHf∘(O2)]\Delta H^{\circ}_f(\text{NO}_2)-\left[\Delta H^{\circ}_f(\text{NO})+\Delta H^{\circ}_f(\text{O}_2)\right]

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