Kinetic Energy Question?

Question

If you have one container of Cl2 gas and an identical container if CH4 gas both at 18 °C, then

A. What is the difference in average kinetic energy of the molecules?
and
B. What is the difference in the average velocity of the molecules?

Answer 1

A) There is no difference in the average kinetic energy of the molecules since they are at the same temperature.

B) The CH4 molecules will have a higher average velocity because they are lighter than Cl2 molecules--16 vs 71 amu. To find out how many times faster, you can take the ratio of the square roots of their masses (Graham's Law).

(71/16)^1/2 = about 2.1

So CH4 molecules have roughly twice the average velocity of Cl2 molecules at the same temperature.