[Geddoe]

Consider the following entities: C2H6, C2H6O, SiHF3, and CH2F2.
(a) Which one will diffuse the fastest?
(b) What is the rms speed (m/s) of the slowest-moving atom or molecule at 25°C?


Any hints and/or thoughts on this question would be helpful, I'm really not sure where to begin when I look at this!

[Borek]

Graham's law, kinetic theory of gases.

[Geddoe]

Graham's law, kinetic theory of gases.

Right on!

I did some further reading on these and I believe I can conclude that the average speed of gas molecules is inversely proportional to the square root of the molar mass. To find the fastest, find the one with the smallest molar mass. 

Therefore:
Molar masses:
C2H6 = 30.068
C2H6O = 46.068
SiHF3 = 86.098
CH2F2 = 52.026

Therefore for (a) I can conclude that C2H6 will diffuse the fastest, correct?

And for (b)...

C2H6 = u=sqrt(3*R*T/M)
= sqrt(3 * 8.314 * 298 / 0.030068)
= 497.1889853

C2H6O =  u=sqrt(3*R*T/M)
= sqrt(3 * 8.314 * 298 / 0.046068)
=  401.6743415

SiHF3 =
sqrt(3 * 8.314 * 298 /0.086098)
= 293.817215

CH2F2 =
sqrt(3 * 8.314 * 298 /0.086098)
= 377.9754138

Therefore SiHF3 is the slowest, did I do this correctly?