Question

12) What is Graham's law of effusion? Explain it in words.

a) Give two formulas representing this law. Which is more commonly used?

b) which postulate of the kinetic molecular theory of gases does this law relate to?

Answer 1

Graham's Law of Effusion

According to Graham’s Law, at constant pressure and temperature, molecules or atoms with lower molecular mass will effuse faster than the higher molecular mass molecules or atoms. Thomas even found out the rate at which they escape through diffusion. In other words, it states that rate of effusion of gas is inversely proportional to the square root of its molecular mass. This formula is generally used while comparing the rates of two different gases at equal pressures and temperatures. Formula can be written as-

Rate1/ Rate2 = √(M2 / M1)

where:

Rate1 is the rate of effusion for the first gas.
Rate2 is the rate of effusion for the second gas.

M1 is the molar mass of gas 1
M2 is the molar mass of gas 2.

Second formula is

more commonly used formula is-

Rate1 / Rate2 = √(M2 /M1)

b) Below postulate of Kinetic theory of gases relates to Graham law:

The average kinetic energy of a collection of gas particles depends on the temperature of the gas and nothing else.