Kinetic Molecular Theory?

Question

Uranium Hexafluoride (UF6) is a much heavier gas than helium , yet a a given temp., the average kinetic energies of the samples of the two gases are the same. Explain.

Shouldn't the heavier gas travel slower? hence reducing KE?

Answer 1

kinetic energy is 1/2 mass*velocity squared

So a large molecule and a small molecule with the same kinetic energies will have different velocities.  

Think of it like this, a truck traveling slowly (let's say 20 mph) and a car that is smaller, but going faster (let's say about 30 mph) and you have to get hit by one.  Which one do you step in front of?  

If they were both going to same speed, you'd take the car because it has less kinetic energy, but when the car goes a little faster the kinetic energies equal out.  In which case you should decide based on the decal on the front of the car.