Question

The standard enthalpy of formation of CH4(g), CO2(g) and H2O(g) are -76.2, -394.8 and -241.6 kJ/mol respectively. Calculate the heat of combustion of methane.

Answer 1

The standard enthalpy of formation of CH4(g), CO2(g) and H2O(g) are -76.2, -394.8 and -241.6 kJ/mol respectively. Calculate the heat of combustion of methane.
Enthalpy of formation = ∆Hf

Combustion of methane equation is:
Ch4(g) + 2O2(g) --> CO2(g) + 2H2O(g)
∆Hc = ∑ ∆Hf(products) - ∑∆Hf(reactants)
= [ ∆Hf(CO2) + 2 ∆Hf(H2O)] -[ ∆Hf(CH4) +2 x ∆Hf(O2)] [enthalpy of formation of O2 = 0]
= [-394.8 + 2 x (-241.6)] -[-76.2 +2 x 0]
= [-394.8 - 483.2] +76.2
= -878 +76.2 = -801.8 kJ/mol