If oxygen, O2, effuses (spreads out) at a rate of 622.0 ms1 under certain conditions of temperature and pressure, how fast will methane, CH4, effuse under the same conditions?

1 Answer
Feb 17, 2016

We know the mass of an O2 molecule is 32 gmol1 and the mass of a CH4 molecule is 16 gmol1, so Graham's Law of Effusion shows that the rate of effusion will be 879.6 ms1.

Explanation:

This question requires Graham's Law of Effusion, which states:

Rate1Rate2=M2M1 where M1 and M2 are the molar masses of the effusing gases.

To make the math easier, let's call the CH4 rate Rate1. (Which we call which doesn't matter, as long as we're consistent: the math will sort itself out!)

Rate1=?
M1=16 gmol1
Rate2=622.0 ms1
M2=32 gmol1

Rearranging:

Rate1=M2M1Rate2
=3216622.0=879.6 ms1