Graham's Law of Effusion is a fundamental principle in chemistry that describes the rate at which gases effuse through a porous material or a small opening. This law, formulated by Thomas Graham in 1848, states that the rate of effusion of a gas is inversely proportional to the square root of its molecular weight. In other words, lighter gases will effuse faster than heavier gases under the same conditions. The law is a direct consequence of the kinetic theory of gases, which describes the behavior of gases in terms of the motion of their molecules.
The mathematical expression of Graham's Law is given by the equation: Rate1 / Rate2 = sqrt(MW2 / MW1), where Rate1 and Rate2 are the rates of effusion of two gases, and MW1 and MW2 are their respective molecular weights. This equation shows that the ratio of the rates of effusion of two gases is equal to the square root of the ratio of their molecular weights. Graham's Law has numerous applications in chemistry and physics, including the separation of gases, the determination of molecular weights, and the study of gas mixtures.
Key Points
- Graham's Law states that the rate of effusion of a gas is inversely proportional to the square root of its molecular weight.
- The law is a direct consequence of the kinetic theory of gases, which describes the behavior of gases in terms of the motion of their molecules.
- The mathematical expression of Graham's Law is given by the equation: Rate1 / Rate2 = sqrt(MW2 / MW1).
- Graham's Law has numerous applications in chemistry and physics, including the separation of gases, the determination of molecular weights, and the study of gas mixtures.
- The law is commonly used in the laboratory to separate gases and to determine the molecular weights of unknown gases.
History and Development of Graham’s Law
Thomas Graham, a Scottish chemist, first proposed the law of effusion in 1848. Graham was studying the diffusion of gases through porous materials and noticed that the rate of diffusion was inversely proportional to the square root of the molecular weight of the gas. He formulated the law based on his experimental observations and published his findings in a paper titled “On the Diffusion of Gases.” Graham’s Law was a significant contribution to the field of chemistry and physics, as it provided a fundamental understanding of the behavior of gases and their interactions with other substances.
Experimental Verification of Graham’s Law
Graham’s Law has been experimentally verified numerous times since its formulation. One of the most common methods of verification is to measure the rate of effusion of two gases through a porous material or a small opening. The rates of effusion are then compared to the predicted values based on the law, and the results are found to be in good agreement. For example, a study published in the Journal of Chemical Education found that the rate of effusion of helium through a porous material was 2.65 times faster than the rate of effusion of oxygen, which is consistent with the predicted value based on Graham’s Law.
| Gas | Molecular Weight | Rate of Effusion |
|---|---|---|
| Helium | 4.003 g/mol | 2.65 cm^3/s |
| Oxygen | 32.00 g/mol | 1.00 cm^3/s |
Applications of Graham’s Law
Graham’s Law has numerous applications in chemistry and physics, including the separation of gases, the determination of molecular weights, and the study of gas mixtures. The law is commonly used in the laboratory to separate gases and to determine the molecular weights of unknown gases. For example, the law can be used to separate a mixture of helium and oxygen by allowing the gases to effuse through a porous material. The rate of effusion of each gas can be measured, and the molecular weights can be calculated based on the law.
Determination of Molecular Weights
Graham’s Law can be used to determine the molecular weights of unknown gases. The law states that the rate of effusion of a gas is inversely proportional to the square root of its molecular weight. By measuring the rate of effusion of a gas and comparing it to the rate of effusion of a known gas, the molecular weight of the unknown gas can be calculated. For example, if the rate of effusion of an unknown gas is 1.50 times faster than the rate of effusion of oxygen, the molecular weight of the unknown gas can be calculated to be 21.33 g/mol.
In conclusion, Graham's Law of Effusion is a fundamental principle in chemistry that describes the rate at which gases effuse through a porous material or a small opening. The law has numerous applications in chemistry and physics, including the separation of gases, the determination of molecular weights, and the study of gas mixtures. By understanding Graham's Law, scientists and engineers can design more efficient gas separation systems and develop new technologies for the analysis and processing of gases.
What is Graham’s Law of Effusion?
+Graham’s Law of Effusion is a fundamental principle in chemistry that describes the rate at which gases effuse through a porous material or a small opening. The law states that the rate of effusion of a gas is inversely proportional to the square root of its molecular weight.
What are the applications of Graham’s Law?
+Graham’s Law has numerous applications in chemistry and physics, including the separation of gases, the determination of molecular weights, and the study of gas mixtures. The law is commonly used in the laboratory to separate gases and to determine the molecular weights of unknown gases.
How is Graham’s Law used to determine molecular weights?
+Graham’s Law can be used to determine the molecular weights of unknown gases by measuring the rate of effusion of the gas and comparing it to the rate of effusion of a known gas. The molecular weight of the unknown gas can be calculated based on the law.