Kinetic Theory

N moles of a polyatomic gas (f=6) must be mixed with two moles of a monoatomic gas so that the mixture behaves as a diatomic gas. The value of N is :

1. 6
2. 2
3. 4
4. 3

Answer

(3) 4

Solution

Degrees of freedom of a mixture: fmix= n1f1+n2f2n1+n2

∵ the mixture acts as diatomic ⇒ fmix=5; monoatomic gas: f=3

5= N(6)+2(3)N+2

5N+10=6N+6

N=4

Answer: (3)