Question

Butane C4 H10 (g),(Delta.Hf = –125.6), combusts in the presence of oxygen to form CO2 (g) (Delta.Hf = –393.5 kJ/mol), and H2 O(g) (Delta.Hf = –241.82) in the reaction:

2 upper C subscript 4 upper H subscript 10 (g) plus 13 upper O subscript 2 (g) right arrow 8 upper C upper O subscript 2 plus 10 upper H subscript 2 upper O (g).

What is the enthalpy of combustion, per mole, of butane?
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..
–5,315 kJ/mol
–2,657.5 kJ/mol
2,657.4 kJ/mol
5,314.8 kJ/mol

Answer 1

ΔHrxn = [8(−393.5) + 10(−241.82)] − [2(−125.6) + 13(0)]
= (−3148.0 − 2418.2) − (−251.2)
= −5566.2 + 251.2
= −5315.0 kJ for 2 mol C4H10

Per mole of butane = −5315.0 / 2 = −2657.5 kJ/mol

Answer: −2,657.5 kJ/mol.