How Does Molecular Weight Affect the Rate of Diffusion?

By Staff WriterLast Updated Apr 13, 2020 3:15:42 AM ET

Molecular weight is indirectly proportional to the rate of diffusion: the smaller, lighter particles disperse faster compared to larger, heavier particles. On average, a particle moves at around 3,997 miles per hour at room temperature.

Diffusion refers to the net arbitrary motion of particles from areas of higher concentration to areas of lower concentration until the concentration gradient reaches an equilibrium state. Diffusion is an important mechanism by which essential molecules are transported in biological systems. Several factors affect the rate of diffusion of particles, including molecular weight, concentration gradient, pressure, temperature and type of solute.

The rate of diffusion has a direct relationship with the concentration gradient, pressure and temperature. The higher the difference between the two concentrations, the faster the rate of diffusion. The same is true for pressure and temperature. The rate of diffusion is inversely proportional to resistance, distance traveled down a concentration gradient and the weight of the molecule.

The molecular weight of a substance is the total weight of all atoms present in the compound. Oxygen, for example, has a molecular weight of 31.999 g/mol, while carbon dioxide has a molecular weight of 44.01 g/mol. Under similar conditions, oxygen diffuses faster than carbon dioxide.