Solution



Back 		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) = -4x kJ

Equate
718 + 872 - 4x = -76
x = 416.5
E (C-H) = 416.5 kJ .