Graham's law

Graham's Law of Effusion (also known as Graham's Law of Diffusion) is a principle in chemistry that describes the rate at which gases diffuse or effuse, being inversely proportional to the square root of their molar masses. This law was formulated by Scottish chemist Thomas Graham in 1848, and it plays a crucial role in the study of gas laws and kinetic theory of gases.

Overview

Graham's Law states that the rate of effusion or diffusion of a gas is inversely proportional to the square root of its molar mass. Mathematically, it can be expressed as:

\[ \frac{\text{Rate of effusion of gas 1}}{\text{Rate of effusion of gas 2}} = \sqrt{\frac{\text{Molar mass of gas 2}}{\text{Molar mass of gas 1}}} \]

This equation implies that lighter gases diffuse or effuse more rapidly than heavier gases. The law is applicable under the assumption that the gases behave ideally and that the temperature and pressure conditions are constant.

Applications

Graham's Law has several practical applications, including:

• Separation of isotopes: It is used in the separation of isotopes by allowing the lighter isotopes to diffuse or effuse faster than the heavier ones.
• Gas purification: The law aids in the purification of gases by diffusing contaminants out of a gas mixture.
• Analytical chemistry: It is utilized in gas chromatography and other analytical techniques to separate and identify gases based on their molar masses.

Historical Context

Thomas Graham conducted experiments that led to the formulation of this law. His work significantly contributed to the understanding of gas behavior and laid the groundwork for the development of the kinetic molecular theory.

Limitations

While Graham's Law provides a useful approximation for the rates of effusion and diffusion of gases, it has limitations. It assumes that gases behave ideally, which is not always the case in real-world conditions. Interactions between gas molecules and deviations from ideal gas behavior can affect the accuracy of predictions made by Graham's Law.

See Also

• Ideal gas law
• Diffusion
• Effusion
• Kinetic theory of gases
• Molar mass