Question

Find the average kinetic energy per molecule at temperature $T$ for an equimolar mixture of two ideal gases $A$ and $B$ where $A$ is monoatomic and $B$ is diatomic.

Answer 1

No. of degrees of freedom per molecule for $A=3$
No. of degrees of freedom per molecule for $B=5$
Since, the mixture is equimolar, the average kinetic energy per molecule will be the simple average of the two values i.e. $\left(\frac{3+5}{2}\right)kT=4kT$, where $k$ is Boltzmann's constant.