KEAM 2021 Physics and Chemistry Solved Paper

Average kinetic energy of n moles of a gas =‌

n

2

fRT
where, f is the degree of freedom.
Since, H2 and N2 both are diatomic in nature, so their degree of freedom will be same.
Number of moles of H2,n1=‌

m1

mH2

where, m1 is given mass =4g and
mH2 is molar mass =2g
⇒‌‌n1=‌

4

2

=‌

2

1

Similarly, number of moles of N2,
n2=‌

m2

mN2

where, m2 is given mass =7g and mN2 is molar mass =28g
⇒
n2=‌

T

28

=‌

1

4

∴ The ratio of kinetic energy of H2 and N2
=‌

‌ n1 2 fRT

n2 2 fRT

=‌

‌ 2 1

1 4

=‌

2

1

×‌

4

1

=8:1