Ethane, a minority component of natural gas, burns to form
carbon dioxide and water according to this reaction:
2H3C−CH3(g)+7O2(g)→4CO2(g)+6H2O(g) Note that the average bond
energy for the breaking of a bond in CO2 is 799 kJ/mol. Use average
bond energies to calculate ΔHrxn for this reaction.
Answer
balanced equation : 2H3C−CH3(g)+7O2(g)→4CO2(g)+6H2O(g)
DH0rxn = 12*DH0d,C-H + 2*DH0d,C-C + 7*DH0d,O=O + 8*DH0f,C=O +
12*DH0f,O-H
= 12*413 + 2*348 +
7*495 +8*(-799) + 12*(-463)
= -2831 kj
