Graham’s law of diffusion explains the connection between the molar masses of gases and the rates at which they diffuse. Thomas Graham, a Scottish chemist, created it in 1833. The process of gas molecules spreading out in response to a gradient in concentration from areas of greater concentration to areas of lower concentration is known as diffusion.
Statement of Graham’s Law
Graham’s law states that:
“Under conditions of constant temperature and pressure, the rate of diffusion (or effusion) of a gas is inversely proportional to the square root of its molar mass.”
Explanation of Graham’s Law
Gas molecules are always moving randomly and crashing into one another as well as the container walls. A gas’s molecular speed, which is influenced by its molar mass, determines how quickly it diffuses. Kinetic theory of gases states that because all gases have the same kinetic energy at a particular temperature, lighter gas molecules move more quickly than heavier ones at that temperature.
Lighter gases (with smaller molar masses) will diffuse more quickly than heavier gases because the speed of gas molecules is proportional to the square root of their molar mass. For example, oxygen (O₂) has a molar mass of around 32 g/mol, whereas hydrogen (H₂), molar mass is about 2 g/mol, will diffuse more quickly.
Diffusion and Effusion
Graham’s law applies not just to diffusion but also to effusion. Process of gas particles entering a vacuum or low-pressure region through a tiny hole or opening is known as diffusion. Lighter gases move more quickly than heavier gases in both effusion and diffusion, however, diffusion refers to the dispersion of gas molecules in an open space, whereas effusion deals with the passage of gas through an opening.
Uses of Graham’s Law
1.Separation of Gases: To separate gases with differing molar masses, apply Graham’s law. For example, Graham’s law was used to separate uranium isotopes during the early stages of nuclear technology development. Diffusion techniques were able to separate uranium-235 (U-235) from uranium-238 (U-238) since the lighter isotope diffused more quickly.
2. Respiratory Physiology: Human physiology also involves Graham’s law. Gases such as carbon dioxide and oxygen diffuse through the alveolar membrane of the lungs. Law explains, why carbon dioxide diffuses out of the blood at a sufficient pace yet oxygen, which has a lower molar mass than carbon dioxide, diffuses into the circulation more quickly.
3. Breath Analysis: Diffusion rates of gases like oxygen and carbon dioxide, medical instruments that detect the gases in a patient’s breath, such as those used to diagnose respiratory diseases rely on Graham’s equation. The comprehension of respiratory function is aided by the variation in diffusion rates.
4. Leak Detection: Graham’s law’s effusion concepts frequently applied by gas leak detectors. To determine the kind of gas and the extent of the leak, a detector can gauge how quickly a gas leaves via a tiny hole and compare that rate to known rates.
Drawbacks of Graham’s Law
Graham’s law has certain drawbacks even if it’s a useful tool for understand gas behavior. It is predicated on the premise that the gases under comparison are ideal gases, which implies that they adhere to all the presumptions of the ideal gas law, such as minimal intermolecular interactions and collisions that are fully elastic.
Graham’s law becomes less accurate at high pressure and low temperatures because real gases actually behave differently from ideal behavior in these situations.
Key statements
Relationship between the molar masses of various gases and the speeds at which they diffuse is made evident and practical by Graham’s law of diffusion. The fact that lighter gases travel faster than heavy gases allows us to forecast and interpret gas behavior in a range of scientific, remedial, and industrial settings.
According to Graham’s law of diffusion, a gas’s rate of diffusion is inversely related to its molar mass squared. It explains why, at constant temperature and pressure, lighter gases diffuse more quickly than heavier ones.
Diffusion refers to the movement of gas molecules from a region of high concentration to a region of low concentration. Effusion refers to the movement of gas molecules through a small opening into a vacuum or low-pressure area. Graham’s law applies to both diffusion and effusion.
Lighter gases have smaller molar masses, means that they have higher molecular speeds at the same temperature. Since Graham’s law states that diffusion is inversely proportional to the square root of molar mass, gases with lower molar masses will diffuse more quickly.
Graham’s law is used in various applications, such as:
Separation of gases, like isotope separation in uranium enrichment.
Medical devices for breath analysis.
Gas leak detection.