Enter the mass of the particles of a gas into the calculator to determine the rate of effusion of the gas.

Effusion Formula

The following formula is used to calculate the rate of effusion.

E ∝ 1 / Sqrt (M)

  • Where E is the rate of effusion/effusion ratio
  • M is the molar mass of the particles (g/mol)

Effusion Definition

In most cases effusion is measured in mL/s, however, this equation results in a unitless number. The reason being that the true effusion rate will depend on the size of the hole, as well as the temperature and pressure of the gas. This equation simply states that the effusion rate is proportional to the inverse of the square root of the mass.

This can be useful in comparing the effusion of two different gases because the proportions to the absolute values will always be the same.

Effusion Example

How to calculate effusion?

  1. First, determine the molar mass.

    Measure the molar mass of the particles.

  2. Next, calculate the effusion ratio.

    Calculate the effusion ratio using the formula above.


What is effusion?

Effusion is the process in which gas escapes a container through a tiny hole into a vacuum. The opening must be smaller than the mean free path of the particles to be considered effusion.