Question

Passage-2
Heat of atomisation is the quantity of heat required to
produce one mole of atoms in the gaseous state from
the element in the standard state is called the heat of
atomisation of the element. The heats of atomisation
of the elements are determined from spectroscopic
measurements and some thermal data.
Answer the following questions based on the
paragraph
A) C + 2H29) CH. AH; = -17.9 Kcal
B) C); 4H; = 170.9 Kcal
C) 2H3 - 4H, AH; = 4 x 52.1 Kcal
Question: Which is/are correct from the above data?
OD​

Answer 1

Explanation:

The heat of atomization of methane is 360 kJ/mol.

This corresponds to breaking of four C−H bonds.

Hence, the heat corresponding to breaking of one C−H bond is

4

360

=90kJ/mol.

The heat of atomization of ethane is 620 kJ/mol.

This corresponds to breaking of one C−C bond and six C−H bonds.

The heat corresponding to breaking of on C-C bond will be 620−6(90)=80 kJ/mol

This corresponds to 1 mole. For one single bond, the required energy that can be obtained by dividing with avogadro's number is given by;

E=

6.02×10

23

80×1000

The energy is related to wavelength by relation E=

λ

hc

Substitute values in the above expression.

6.02×10

23

80×1000

=

λ

6.62×10

−34

×3×10

8

Hence, λ=1.49×10

−6

m=1.49×10

3

nm