First slide

Enthalpy of Atomisation and bond dissociation

Question

Statement I : Bond length in C–C > N–N > O–O
Statement II : Bond enthalpy in C–C > N–N > O–O

Difficult

A

Both statements I and II are correct
B

Statement - I is correct and statement - II is incorrect
C

Statement - I is incorrect and statement - II is correct
D

Both statements I and II are incorrect

Solution

Left to right in a period Atomic radius decreases
$∴ size of C > N > O$
$∴ C - C > N - N > O - O \dots . . Bond length$
Generally
$Bond enthalpy \propto \frac{1}{Bond length}$
$∴ Expected trend of Bond enthalpy$
C–C < N–N < O–O
But both ‘N’ and ‘O’ contain lone pairs. Due to the repulsions between lone pairs of adjacent atoms in N–N and O–O their bond enthalpies are very low.
$∴ Experimental bond enthalpy$
C–C > N–N > O–O

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