Chemistry

Chemistry

Problem

Combustion of four gaseous hydrocarbons at 25 ∘C25\,^{\circ}\text{C} and 1 bar produces liquid water as shown below. A. CH4(g)+2 O2(g)→CO2(g)+2 H2O(l)\text{CH}_4(g)+2\,\text{O}_2(g)\rightarrow\text{CO}_2(g)+2\,\text{H}_2\text{O}(l) B. C2H6(g)+72 O2(g)→2 CO2(g)+3 H2O(l)\text{C}_2\text{H}_6(g)+\tfrac{7}{2}\,\text{O}_2(g)\rightarrow2\,\text{CO}_2(g)+3\,\text{H}_2\text{O}(l) C. C3H8(g)+5 O2(g)→3 CO2(g)+4 H2O(l)\text{C}_3\text{H}_8(g)+5\,\text{O}_2(g)\rightarrow3\,\text{CO}_2(g)+4\,\text{H}_2\text{O}(l) D. C4H10(g)+132 O2(g)→4 CO2(g)+5 H2O(l)\text{C}_4\text{H}_{10}(g)+\tfrac{13}{2}\,\text{O}_2(g)\rightarrow4\,\text{CO}_2(g)+5\,\text{H}_2\text{O}(l) Standard enthalpies of formation (in kJ mol−1\text{kJ mol}^{-1}): ΔHf∘(CO2,g)=−393.5\Delta H_f^{\circ}(\text{CO}_2,g)=-393.5, ΔHf∘(H2O,l)=−285.8\Delta H_f^{\circ}(\text{H}_2\text{O},l)=-285.8, ΔHf∘(CH4,g)=−74.8\Delta H_f^{\circ}(\text{CH}_4,g)=-74.8, ΔHf∘(C2H6,g)=−84.7\Delta H_f^{\circ}(\text{C}_2\text{H}_6,g)=-84.7, ΔHf∘(C3H8,g)=−104.7\Delta H_f^{\circ}(\text{C}_3\text{H}_8,g)=-104.7, ΔHf∘(C4H10,g)=−125.6\Delta H_f^{\circ}(\text{C}_4\text{H}_{10},g)=-125.6. Which combustion reaction releases the greatest amount of heat per mole of fuel burned (i.e., has the most negative ΔHrxn∘\Delta H^{\circ}_{\text{rxn}})? a) Reaction B b) Reaction C c) Reaction D d) Reaction A

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