The reaction has

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

Problem

The reaction 2H2(g)+O2(g)→2H2O(g)2\text{H}_2(g)+\text{O}_2(g)\rightarrow 2\text{H}_2\text{O}(g) has ΔHrxn∘=−484 kJ\Delta H^\circ_{\text{rxn}}=-484\,\text{kJ}. Given ΔHf∘(H2(g))=0\Delta H_f^\circ\bigl(\text{H}_2(g)\bigr)=0 and ΔHf∘(O2(g))=0\Delta H_f^\circ\bigl(\text{O}_2(g)\bigr)=0, what is ΔHf∘\Delta H_f^\circ for H2O(g)\text{H}_2\text{O}(g)? (a) −484 kJ mol−1-484\,\text{kJ mol}^{-1} (b) −242 kJ mol−1-242\,\text{kJ mol}^{-1} (c) +242 kJ mol−1+242\,\text{kJ mol}^{-1} (d) −121 kJ mol−1-121\,\text{kJ mol}^{-1}

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