Answer to Question #99586 in General Chemistry for Beverlie

Question

Brazilians are quite familiar with fueling their automobiles with ethanol, a fermentation product from sugarcane.
C2H5OH(l) +3O2(g) = 2CO2(g)+3H2O(g)
Calculate the standard molar enthalpy for the complete combustion of liquid ethanol (C2H5OH) using the standard enthalpies of formation of the reactants and products. ansswer in kj

Answer 1

Hess's law state :ΔH⁰_(reaction)=$\sum$ ΔH_f⁰_(products) - $\sum$ ΔH_f⁰_(reactants)where  ΔH_f is an enthalpy of formation, the ⁰ - superscript indicates standard state values.

∑ ΔH_f⁰_(reactants)= ΔH_f⁰(C₂H₅OH) + ΔH_f⁰(O₂)The enthalpy of formation of a simple substance is 0.$\implies$ ∑ ΔH_f⁰_(reactants)= ΔH_f⁰(C₂H₅OH)ΔH_f⁰(C₂H₅OH)=– 277,6 kJ/mole

∑ ΔH_f⁰_(products)= 2 * ΔH_f⁰(CO₂) + 3 * ΔH_f⁰(H₂O)ΔH_f⁰(CO₂)=– 393,5 kJ/moleΔH_f⁰(H₂O)_(gase)= –241.8 kJ/mole∑ ΔH_f⁰_(products) = -1512,4 kJ/moleΔH⁰_(reaction)=-1234,8 kJ/mole

[reference (table) values ΔH_f⁰_(products) ]