Answer to Question #110171 in General Chemistry for Kewl

Question

Calculate the enthalpy of combustion of methane CH4 + O2 --> CO2 + H2O

Answer 1

CH4 + 2 O2 --> CO2 + 2 H2O

Standard enthalpy of reaction $\Delta$H⁰r is the sum of formation enthalpies of the products minus the sum of formation enthalpies of reactants. Using the thermodynamic tables of standard formation enthaplies, one finds that:

$\Delta$H⁰r = ΔH⁰f(CO2) + 2*ΔH⁰f(H2O) - ΔH⁰f(CH4) - 2*ΔH⁰f(O2) =

= -393.5 + (-2*285.8) - 2*0 - (-74.9) = -890.2 kJ

Answer: entalpy of combustion is -890.2 kJ