For the reaction

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

Problem

For the reaction 2NO(g)+O2(g)→2NO2(g)2\text{NO}(g)+\text{O}_2(g)\rightarrow 2\text{NO}_2(g), which of the following algebraic expressions gives the standard enthalpy change ΔHrxn∘\Delta H^{\circ}_{\text{rxn}} in terms of standard enthalpies of formation ΔHf∘\Delta H_f^{\circ}? (a) ΔH∘=[2 ΔHf∘(NO)+ΔHf∘(O2)]−2 ΔHf∘(NO2)\Delta H^{\circ}=\left[2\,\Delta H_f^{\circ}(\text{NO})+\Delta H_f^{\circ}(\text{O}_2)\right]-2\,\Delta H_f^{\circ}(\text{NO}_2) (b) ΔH∘=ΔHf∘(NO2)−[ΔHf∘(NO)+ΔHf∘(O2)]\Delta H^{\circ}=\Delta H_f^{\circ}(\text{NO}_2)-\left[\Delta H_f^{\circ}(\text{NO})+\Delta H_f^{\circ}(\text{O}_2)\right] (c) ΔH∘=2 ΔHf∘(NO2)−[2 ΔHf∘(NO)+ΔHf∘(O2)]\Delta H^{\circ}=2\,\Delta H_f^{\circ}(\text{NO}_2)-\left[2\,\Delta H_f^{\circ}(\text{NO})+\Delta H_f^{\circ}(\text{O}_2)\right] (d) ΔH∘=2 ΔHf∘(NO2)−[2 ΔHf∘(NO)+2 ΔHf∘(O2)]\Delta H^{\circ}=2\,\Delta H_f^{\circ}(\text{NO}_2)-\left[2\,\Delta H_f^{\circ}(\text{NO})+2\,\Delta H_f^{\circ}(\text{O}_2)\right]

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