The key difference between Graham’s law of effusion and diffusion is that Graham’s law of effusion is applied for a gas that passes through an opening that is smaller than the gas particles whereas Graham’s law of diffusion is applied for gas molecules that disperse throughout a container.
Graham’s law states that the rate of diffusion or effusion of a gas is inversely proportional to the square root of its molar mass. This law was developed by the physical chemist Thomas Graham in 1848.
CONTENTS
1. Overview and Key Difference
2. What is Graham’s Law of Effusion
3. What is Graham’s Law of Diffusion
5. Side by Side Comparison – Graham’s Law of Effusion and Diffusion in Tabular Form
6. Summary
What is Graham’s Law of Effusion?
Graham’s law of effusion indicates that the rate of diffusion or effusion of a gas is inversely proportional to the square root of its molar mass. We can give this law as a mathematic expression as follows;
In this mathematic expression, rate1 is the rate of effusion of a gas; rate2 is the rate of effusion for a second gas; M1 is the molar mass of first gas while M2 is the molar mass of the second gas. According to this relationship, if the molar mass of one gas is four times the molar mass of another gas, it diffuses through a porous plug at half the rate of the other gas. Graham’s law is the basis for separating isotopes by diffusion (important in the production of the atomic bomb).
For molecular effusion of gases which involves the movement of one gas at a time through a hole, Graham’s law is the most accurate theory for the calculation of the rate of the gas leakage. However, it is only approximately accurate for the diffusion of one gas in another gas since it includes the movement of one gas into another gas.
What is Graham’s Law of Diffusion?
Graham’s law of diffusion is a law in chemistry which indicates that the rate of diffusion or effusion of a gas is inversely proportional to the square root of its molar mass. When we are applying this law for the diffusion of a gas, first we need to know what is diffusion. Diffusion refers to the gradual mixing of gases due to the motion of gas particles in the absence of mechanical agitation such as stirring.
Figure 01: Diffusion
This law is only approximately accurate for the diffusion of one gas in another gas (because it includes the movement of one gas into another gas).
What is the Difference Between Graham’s Law of Effusion and Diffusion?
Graham’s law states that the rate of diffusion or effusion of a gas is inversely proportional to the square root of its molar mass. The key difference between Graham’s law of effusion and diffusion is that Graham’s law of effusion is applied for a gas that passes through an opening that smaller than the gas particles whereas Graham’s law of diffusion is applied for gas molecules that disperse throughout a container. Besides, Graham’s law of effusion is the most accurate law for effusion while Graham’s law of diffusion is only approximately accurate for diffusion.
Below infographic summarizes the difference between Graham’s law of effusion and diffusion.
Summary – Graham’s Law of Effusion vs Diffusion
Graham’s law states that the rate of diffusion or effusion of a gas is inversely proportional to the square root of its molar mass. The key difference between Graham’s law of effusion and diffusion is that Graham’s law of effusion is applied for a gas that passes through an opening that smaller than the gas particles whereas Graham’s law of diffusion is applied for gas molecules that disperse throughout a container.
Reference:
1. “2.9: Graham’s Laws of Diffusion and Effusion.” Chemistry LibreTexts, Libretexts, 14 July 2020, Available here.
Image Courtesy:
1. “Diffusion” By JrPol – Own work (CC BY 3.0) via Commons Wikimedia