Rate₁ / Rate₂ = √(M₂ / M₁)
Time₁ / Time₂ = √(M₁ / M₂)
Where M₁ and M₂ are the molar masses of the two gases. Lighter gases effuse faster.
Click a gas to fill in the molar mass field
Graham's Law of Effusion, discovered by Scottish chemist Thomas Graham in 1848, describes the relationship between the rate at which gases escape through a small opening (effusion) and their molar masses. The law states that the rate of effusion of a gas is inversely proportional to the square root of its molar mass. This means lighter gases effuse faster than heavier gases.
Effusion is the process by which gas molecules pass through a tiny opening into a vacuum or lower pressure region. This is different from diffusion, which is the spreading of gas molecules throughout a space. However, Graham's Law applies to both processes under ideal conditions.
Uranium Enrichment
Graham's Law is used in gaseous diffusion plants to separate uranium isotopes (U-235 and U-238) in the form of uranium hexafluoride gas.
Leak Detection
Helium, being a light gas, effuses quickly and is used to detect leaks in vacuum systems and sealed containers.
Gas Identification
By measuring effusion rates, unknown gases can be identified by comparing them to gases with known molar masses.
Balloon Deflation
Helium balloons deflate faster than air-filled balloons because helium effuses through the balloon material more quickly.
Note: Graham's Law applies to ideal gases under identical conditions. Real gas behavior may deviate due to intermolecular forces or non-ideal conditions.