Graham's Law

Definition

Graham's Law is a fundamental principle in chemistry that describes the relationship between the rates of effusion and diffusion of gases. It states that the rates of effusion or diffusion of gases are inversely proportional to the square roots of their molar masses.

5 Must Know Facts For Your Next Test

1. Graham's Law states that the rates of effusion or diffusion of gases are inversely proportional to the square roots of their molar masses.
2. The rate of effusion or diffusion is directly proportional to the average kinetic energy of the gas molecules, which is determined by their temperature.
3. Graham's Law is an important principle in understanding the behavior of gases and their transport properties, such as in the design of separation techniques like fractional distillation.
4. The law is named after the Scottish chemist Thomas Graham, who first observed and formulated the relationship between the rates of effusion and the molar masses of gases.
5. Graham's Law is a key concept in the Kinetic-Molecular Theory, which provides a framework for understanding the behavior of gases at the molecular level.

Review Questions

• Explain how Graham's Law relates to the process of effusion and diffusion of gases.
  • Graham's Law states that the rates of effusion or diffusion of gases are inversely proportional to the square roots of their molar masses. This means that gases with lower molar masses will effuse or diffuse faster than gases with higher molar masses, all other factors being equal. This is because the average kinetic energy of the gas molecules, which determines their rate of movement, is inversely related to the square root of their molar mass. This relationship is a fundamental principle in understanding the behavior of gases and their transport properties.
• Describe how Graham's Law is connected to the Kinetic-Molecular Theory of gases.
  • The Kinetic-Molecular Theory provides a framework for understanding the behavior of gases at the molecular level, and Graham's Law is a key concept within this theory. The Kinetic-Molecular Theory states that gases are composed of constantly moving, independent molecules, and that the average kinetic energy of these molecules is directly related to the temperature of the gas. Graham's Law builds upon this by demonstrating that the rates of effusion and diffusion of gases are inversely proportional to the square roots of their molar masses, which is a direct consequence of the random thermal motion of the gas molecules as described by the Kinetic-Molecular Theory.
• Analyze how the principles of Graham's Law can be applied to the design and operation of separation techniques, such as fractional distillation.
  • The principles of Graham's Law can be applied to the design and operation of separation techniques, such as fractional distillation, which is used to separate a mixture of gases or liquids with different boiling points. In fractional distillation, the different components of the mixture are vaporized and then condensed at different temperatures, allowing for their separation. Graham's Law is relevant here because the rates of effusion and diffusion of the different gas components will be inversely proportional to the square roots of their molar masses. This means that the lighter, lower molar mass components will be able to escape the liquid mixture and reach the condensation stage more quickly than the heavier, higher molar mass components, enabling their separation. By understanding and applying the principles of Graham's Law, engineers and scientists can optimize the design and operation of fractional distillation and other separation techniques.

Related terms

Effusion:

The process by which gas molecules escape from a container through a small opening, driven by the pressure difference between the container and the surrounding environment.

Diffusion:

The spontaneous movement of particles from a region of higher concentration to a region of lower concentration, driven by the random thermal motion of the particles.

Kinetic-Molecular Theory:

A theory that explains the behavior of gases in terms of the motion and interactions of their constituent molecules, including the concepts of temperature, pressure, and the relationship between them.