Question

The enthalpies of formation of the compounds in the combustion of methane,

Upper C upper H subscript 4 (g) plus 2 upper O subscript 2 (g) right arrow upper C upper o subscript 2 (g) plus 2 upper H subscript 2 upper O (g).,

are CH4 (g): Delta.Hf = –74.6 kJ/mol; CO2 (g): Delta.Hf = –393.5 kJ/mol; and H2 O(g): Delta.Hf = –241.82 kJ/mol.

How much heat is released by the combustion of 2 mol of methane?
Use Delta H r x n equals the sum of delta H f of all the products minus the sum of delta H f of all the reactants..
mc018-6.jpg80.3 kJ
mc018-7.jpg802.5 kJ
mc018-8.jpg1,605.1 kJ
mc018-9.jpg6,420.3 kJ

Answer 1

ΔHrxn per mole CH4 = [ΔHf(CO2) + 2ΔHf(H2O)] − [ΔHf(CH4) + 2ΔHf(O2)]
= [−393.5 + 2(−241.82)] − [−74.6 + 0]
= −802.54 kJ per mol CH4.

For 2 mol CH4: ΔH = 2(−802.54) = −1605.08 kJ.

So 1,605.1 kJ of heat is released (ΔH = −1,605.1 kJ).