Question

Calculate the approximate enthalpy change, δhrxn, for the combustion of one mole of methane a shown in the balanced chemical equation: ch4+2o2→2h2o+co2 use the values you calculated in parts a, b, c, and d, keeping in mind the stoichiometric coefficients

Answer 1

To solve for the enthalpy of reaction, we apply the Hess's Law.

ΔHrxn = ∑(ν×Hf of products) - ∑(ν×Hf of reactants)
where
v is the stoichiometric coefficient determined from the balanced reaction
Hf is the standard heat of formation; these are empirical values:
*For CH₄: Hf = −74.87 kJ/mol
*For O₂: Hf = 0
*For CO₂: -393.5 kJ/mol 
*For H₂O: -241.82 kJ/mol

ΔHrxn = [(2*-241.82 kJ/mol)+(1*-393.5 kJ/mol)] - [(1*−74.87 kJ/mol)+(2*0 kJ/mol)] = -802.27 kJ/mol