Use the following enthalpy data

CHEMISTRY · Subjective · A Level · Chemistry · Energetics · Energetics

Problem

Use the following enthalpy data, measured at the same temperature and pressure: (i)

\; \text{X}(g) + \text{Y}(g) \rightarrow \text{XY}(g) \quad \Delta H_1 = -120\;\text{kJ}

(ii)

\; \tfrac{1}{2}\text{X}_2(g) \rightarrow \text{X}(g) \quad \Delta H_2 = +80\;\text{kJ}

(iii)

\; \tfrac{1}{2}\text{Y}_2(g) \rightarrow \text{Y}(g) \quad \Delta H_3 = +50\;\text{kJ}

Calculate the enthalpy change, in kilojoules, for the reaction

\text{X}_2(g) + \text{Y}_2(g) \rightarrow 2\,\text{XY}(g)