Effusion is the term used to describe the passage of a gas through a tiny
orifice into an evacuated chamber. The rate of effusion measures the speed at
which the gas is transferred into the chamber.
TIP
Effusion means passing of a gas through an orifice (like through the neck of a balloon).GAS LAWS AND RELATED PROBLEMS
Graham’s Law of Effusion (Diffusion)
This law relates the rate at which a gas diffuses (or effuses) to the type of
molecule in the gas. It can be expressed as follows:
The Rate of Effusion of a Gas Is Inversely Proportional to the Square Root
of its Molecular Mass.Hydrogen, with the lowest molecular mass, can diffuse more rapidly than
other gases under similar conditions.
Type Problem
Compare the rate of diffusion of hydrogen to that of oxygen under similar
conditions.
The formula is
TIP
Know how to use Graham’s Law of Effusion.Let A be H 2 and B be O 2.Therefore hydrogen diffuses four times as fast as oxygen.
In dealing with the gas laws, a student must know what is meant by standard