Skip over navigation

Kinetic Molecular Theory

Problems

Kinetic Molecular Theory and Its Applications

How to Cite This SparkNote

Problem : Samples of H 2 and He are at the same temperature. What is the ratio of their average velocities?

The molar mass of H 2 is half that of He. The temperatures of the two samples are the same, so their kinetic energies are the same. This leads to the following equation:

M H2 (V H2 )2 = M He(V He)2    

Rearranging and solving this equation, we find that = .

Problem : A volume of H 2 and an identical volume of O 2 are at the same temperature. Plot the Maxwell-Boltzmann speed distributions for the two gases on the same graph.

Problem : Calculate $v_{\mbox{rms}}$ for a sample of O 2 at 300 K.


v rms =  
  =  
  = 480m/s  

Remember that M must be in !

Problem : Rank v rms , , and v p in order of increasing speed.

v p < < v rms

Problem : Calculate the ratio of the rates of effusion of H 2 over He.


=  
  =  

Note that this exactly mirrors the ratio of the average velocities of the two gases.

Follow Us