Question

The combustion of methane gas (ch4) forms co2(g)+ h2o(ℓ). calculate the heat produced by burning 2 mol of the methane gas. use these ∆h0 f data to help: ch4(g)= -74.9 kj/mol co2(g)= -393.5kj/mol h2o(ℓ)= -285.8kj/mol. answer in units of kj.

Answer 1

Hess's Law is as follows. Note: Google Hess's law for the actual formula (i.e. with the Greek characters). ΔH(reaction) = Sum of ΔH(formation of products) - Sum of ΔH(formation of reactants) Now determine you're formula/reaction. In this case it's as follows: CH4 + 2 O2 -----> CO2 + 2 H2O The ΔH(formation) can be found in standardized tables, either online, in books, or provided to you. The ΔH you need for this is as follows in kJ/mol: CH4 (g) -75 O2 (g) 0 CO2 (g) -394 H2O (l) -286 When you plug the info into the formula you get the following: ΔH(reaction) = [(2*-238) + -394)] - [-75 + (2*0)] ΔH(reaction) = -891 kJ/mol Now you're looking for the amount of kJ for 1.65 mol. Your standard formula is as follows: E = ΔH(reaction) * mol where E is energy measured in kJ. So when you plug in your relevant values you get: E = -891 * 1.65 E = -1470.15 kJ