Solution
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The equation for heat of combustion of methane is written first:
(
= -890 kJ) (given in question).
Required
= -394 kJ
= -572 kJ
= +890 kJ
= -76 kJ
Use bond energy values
= 718 kJ
Breaking 2 mole H-H = 2(436) = 872 kJ
Forming 4 mole C-H = 4(-
x
) = -4
x
kJ
Equate
718 + 872 - 4
x
= -76
x
= 416.5
E (C-H) = 416.5 kJ
.