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30/09/2021 11:30 am
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The enthalpy of atomisation of CH4 and C2H6 are 360 and 620 kcal mol-1 respectively. The C – C bond energy is expected to be
(a) 210 kcal mol-1
(b) 80 kcal mol-1
(c) 130 kcal mol-1
(d) 180 kcal mol-1
1 Answer
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30/09/2021 11:36 am
Correct answer: (b) 80 kcal mol-1
Explanation:
Atomisation of methane
CH4(g) → C(g) + 4H(g);
ΔH = 360 kcal
∴ C - H bond energy = \(\frac{360}{4}\)
= 90 kcal mol-1
C2H6(g) → 2C(g) + 6H(g);
ΔH = 620 kcal
or HC-C + 6HC-H = 620
∴ HC-C = 620 - 6HC-H
= 620 - 6 x 90
= 80 kcal mol-1