# The Relationship Between Rate of Diffusion and Molecular Weight of Gas

## Which of the following statements is true?

1. The square root of the molecular weight of a gas is equal to its rate of diffusion.

2. The rate of diffusion of a gas in inversely proportional to the square root of its molecular weight.

3. The rate of diffusion of a gas is directly proportional to the square root of its molecular weight.

4. The square root of the molecular weight of a gas is not related to its rate of diffusion.

## Answer:

The rate of diffusion of a gas is inversely proportional to the square root of its molecular weight.

Scottish chemist Thomas Graham made a major contribution to the study of the diffusion of gases and liquids in the 19th century. He observed that when a gas diffuses through another gaseous medium, the density of this gas directly interferes with the speed of diffusion.

Therefore, according to Graham's Law, the speed of diffusion (ability of a gas to "spread" in an area or container) and effusion (ability of a gas to escape from one environment to another) is inversely proportional to the square root of its density. This means that the less dense the gas, the greater its speed of diffusion and effusion and vice versa.

Graham's Law can be expressed mathematically as follows: V1/V2 = √(d1/d2) where V = Volume of gases and d = density of gases