dalton and grahams law

Question

1. At STP which of the following gases will diffuse most rapidly? Explain your answer

                   H₂ , F₂, Ne  Xe

2. Under the same conditions of temperature and pressure, rank the following gas in decreasing order of rate of diffusion? 

                  H₂. CH₄, He, NH₃

Answer 1

Graham's law in a nutshell says that the lighter gas diffuses faster. So H2 is the fastest to diffuse. As an explanation: This law stems from the fact that there is a relationship between temperature and the average kinetic energy of the system.

T ∼ avg KE (~ here is related to).

The gases are in the same system so the Temperature is the same.

A definition of Kinetic Energy is KE = .5mv^2

So for all the gases to have the same average kinetic energy the lighter gases must move faster. (small m, big v).

This is important for the second part. If we want to rank them in decreasing order of diffusion we should rank them in increasing order of molar mass. So the answer would be:

H2 (2 amu), He (4 amu), CH4 (16 amu), NH3 (17 amu)