Question

Propane (C3 H8 (g), Delta.Hf = –103.8 kJ/mol) reacts with oxygen to produce carbon dioxide (CO2 , Delta.Hf = –393.5 kJ/mol ) and water (H2 O, Delta.Hf = –241.82 kJ/mol) according to the equation below.

Upper C subscript 3 upper H subscript 8 (g) plus 5 upper O subscript 2 (g) right arrow 3 upper C upper O subscript 2 (g) plus 4 upper H subscript 2 upper O (g).

What is the enthalpy of combustion (per mole) of C3 H8 (g)?
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..
–2,044.0 kJ/mol
–531.5 kJ/mol
531.5 kJ/mol
2,044.0 kJ/mol

Answer 1

ΔHrxn = [3(−393.5) + 4(−241.82)] − [1(−103.8) + 5(0)]
= (−1180.5 − 967.28) − (−103.8)
= −2147.78 + 103.8
= −2043.98 ≈ −2,044.0 kJ/mol

Answer: −2,044.0 kJ/mol (the combustion is exothermic).