Example Problem: TBE

o Determine the enthalpy change that accompanies the reaction below. Use the method of average bond dissociation energies to determine the answer

4 x 414 + 0.5 x 498 = 1905 kJ/mol for bonds broken (this always costs energy, +ve sign)

3 x 414 + 351 + 464 = 2057 kJ/mol for bonds formed (this always releases energy, -ve sign)

ΔHrxn = 1905 – 2057 = -152 kJ/mol for the formation of methanol from methane and oxygen

o What does this tell us about the heat content of methanol as a fuel compared to that of methane (natural gas)?

124 2 3

12

CH ( ) O ( ) CH OH( )

: 4(C-H) (O=O) 3(C-H) 1(C-O) 1(O-H)

g g g

TBE

124 2 3CH ( ) O ( ) CH OH( )g g g