temperatures, T 1 and T 2 , where T 2 > T 1 . Notice that the bell-shaped curve flattens and shifts to the
right as the temperature increases, indicating that at higher temperatures more molecules are
moving at high speeds. The area under the curve is the total number of gas molecules and thus has
to remain constant even as the shape of the curve changes.
BASIC CONCEPT
For gases of the same molecules, the higher the temperature, the higher the kinetic energy,
and thus the higher the average speed of the molecules.GRAHAM’S LAW OF DIFFUSION AND EFFUSION
The typical speed of a gas molecule in room temperature is quite high. If, however, a bottle of
perfume at the center of a room is opened while you are standing in a corner, the time lapse
between the opening of the bottle and when you can detect the smell may be longer than what
would be expected from the molecular speed. This is because the perfume molecules are constantly
colliding with air molecules that change their course in a random fashion. This process in which gas
molecules move through a mixture is known as diffusion (although this term is not limited to the
gaseous phase). Effusion, on the other hand, is the flow of gas particles under pressure from one
compartment to another through a small opening. The kinetic molecular theory of gases predicted
that heavier gas molecules move more slowly than lighter ones under the same conditions. Under
isothermal (same temperature) and isobaric (same pressure) conditions, the rates at which two
gases diffuse and effuse follow the same mathematical rule and are inversely proportional to the
square root of their molar masses: