In chemistry,'effusion is the process in which individual molecules flow through a hole without collisions between molecules. This occurs if the diameter of the hole is considerably smaller than the mean free path of the molecules.^[1] According to Graham's law, the rate at which gases effuse (i.e., how many molecules pass through the hole per second) is dependent on their molecular weight; gases with a lower molecular weight effuse more quickly than gases with a higher molecular weight. For two gases at the same temperature (and having the same specific heat), and thus having the same kinetic energy, the root mean square molecular speed, v_rms, of each gas can be found using the equation

³⁄₂k_BT = ¹⁄₂mv2rms

where k_B is the Boltzmann constant. Thus, lighter molecules have a higher speed. This results in more molecules passing through the hole per unit time. This is why a balloon filled with low molecular weight hydrogen left alone for a reasonable amount of time deflates faster than an equivalent balloon full of higher molecular weight oxygen.

[edit] See also

• Graham's Law of Effusion
• Diffusion

[edit] References

[edit] External links

• Graham's law