Question

A sample of helium gas is at a temperature of 300 K and a pressure of 0.5 atm. What is the average kinetic energy of a molecule of a gas?

Answer 1

Average kinetic energy of an ideal gas is equal to its thermal energy. Since, for helium, degrees of freedom is 3 as there is only translational motion possible in three directions. Hence,

$KE=U=\frac{f}{2}kT=\frac{3}{2}\left(1.3807X{10}^{-23}\right)\left(300\right)=6.21X{10}^{-21}J$

Answer is $6.21X{10}^{-21}J$