Question

If enthalpies of methane and ethane are respectively 320 and 360 calories then the bond energy of C – C bond is

• A. 80 calories
• B. 40 calories
• C. 60 calories
• D. – 120 calories

Answer 1

Answer: (D)

– 120 calories

Answer 2

$CH_{4} \rightarrow 4C - H;$ $\Delta H = 320$

$1E_{C - H} = \frac{320}{4} = 80$ calories then $6E_{C - H} = 480cal.$

$C_{2}H_{6} \rightarrow E_{C - C} + 6E_{C - H};\Delta H = 360cal.$

$360 = E_{C - C} + 480$

$E_{C - C} = 360 - 480 = - 120cal$