The dissociation energy of methane is 360 k cal/mol and that of ethane is 620 kcal mol $^{- 1}$ the bond energy of one mole C-C bonds is (in k cal)

210

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Solution

The correct option is D 80
For one mole methane (contains 4 C-H bonds ), dissociation energy is 360 kJ
which means,
a.
$(4 \times B o n d e n e r g y o f C - H b o n d) (N_{A}) = 360 k J$

For one mole ethane (contains 6 C-H bonds and 1 C-C bond ), dissociation energy is 360 kJ
which means,
b.
$(6 \times B o n d e n e r g y o f C - H b o n d + B o n d e n e r g y o f C - C b o n d) (N_{A}) = 620 k J$

After multiplying equation a with 3 and equation b with 2,we get;

c.
$(12 \times B o n d e n e r g y o f C - H b o n d) (N_{A}) = 1080 k J$

d.
$(12 \times B o n d e n e r g y o f C - H b o n d + 2 \times B o n d e n e r g y o f C - C b o n d) (N_{A}) = 1240 k J$

subtracting equation c from d, we get;
$2 \times B o n d e n e r g y o f C - C b o n d = 160 k J$

$B o n d e n e r g y o f C - C b o n d = 80 k J$

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