Can someone explain this chemistry problem??

Question

can someone explain to me how to do this problem step by step??

Methan CH4 and propane C3H8 are 2 components of the natural gas burned in Bunsen burners. If a methane molecule travels at 675 m/s from a gas jet, how fast does the propane molecule travel?

Answer 1

The dffusion rate of a gas varies inversely with the square root of  its mass

      R= 1/SQRT ( M)  so a relative rate of diffusion would be a comparison of the diffusion rates              

           R1/R2= 1/SQRT (M1) / 1/SQRT(M2)

                     mass of CH4 = 16 mass ,of propane = 44

so R1= 1/SQRT(16) =  0.25     R2 = 1/SQRT(44) = 0.1515

so CH4 diffuses 0.25/0.1515 = 1.667 times faster than propane

OR  propane diffuses 0.1515/0.25 = 0.606 times as fast as CH4

so if methane diffuses at a rate of 675 m/sec  then propane diffuses at a rate of 675x 0.606 = 409.5 m/sec

Answer 2

http://en.wikipedia.org/wiki/Graham%27s_...

i.e the more massive it is the slower it travels

rate 1 / rate 2 = (MW2 / MW1)^1/2

675 / rate 2 = [( 44.1 g/mol C3H8)/ (16.04 g/mol CH4)]^1/2

675 / rate 2 = [2.75]1/2

675 / rate 2 = 1.66

rate = 675 / 1.66

your answer is 407m/s