Three reactions and their standard enthalpy changes are listed below

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

Problem

Three reactions and their standard enthalpy changes are listed below. I. 2 H2(g)+O2(g)→2 H2O(l)            ΔH∘=−571.6 kJ2\,\text{H}_2(g)+\text{O}_2(g)\rightarrow2\,\text{H}_2\text{O}(l)\qquad\;\;\;\;\;\;\Delta H^{\circ}=-571.6\,\text{kJ} II. N2(g)+3 H2(g)→2 NH3(g)ΔH∘=−92.4 kJ\text{N}_2(g)+3\,\text{H}_2(g)\rightarrow2\,\text{NH}_3(g)\qquad\qquad\Delta H^{\circ}=-92.4\,\text{kJ} III. CaCO3(s)→CaO(s)+CO2(g)ΔH∘=+178.0 kJ\text{CaCO}_3(s)\rightarrow\text{CaO}(s)+\text{CO}_2(g)\qquad\quad\Delta H^{\circ}=+178.0\,\text{kJ} Which ranking correctly orders the reactions from most exothermic to most endothermic? (a) II > I > III (b) I > II > III (c) I > III > II (d) III > II > I

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