The average kinetic energy per molecule of an ideal gas is always equal to

In equilibrium, the average kinetic energy of molecules of different gases will be equal. That is 

$\frac{1}{2}{m}_1{v_1}^2 = \frac{1}{2}{m}_2{v_2}^2 = \left(\frac{3}{2}{k}_{B}T\right)$