How does molecular size affect the rate of diffusion?

Molecular size inversely affects the rate of diffusion; larger molecules diffuse slower than smaller ones.

Diffusion is the process by which particles spread out from an area of high concentration to an area of low concentration. It's a fundamental concept in chemistry and is driven by the random motion of particles. The rate of diffusion is influenced by several factors, one of which is the size of the molecules involved.

Larger molecules move slower than smaller ones because they have more mass. This means that they require more energy to move, which slows down their rate of diffusion. For example, a molecule of oxygen (O2) will diffuse faster than a molecule of carbon dioxide (CO2) because oxygen is smaller and lighter than carbon dioxide. This principle is known as Graham's law of diffusion, which states that the rate of diffusion of a gas is inversely proportional to the square root of its molar mass.

In addition, larger molecules are more likely to collide with other molecules, which can also slow down their rate of diffusion. These collisions can cause the molecules to change direction, which can slow down their overall movement from an area of high concentration to an area of low concentration.

In conclusion, the size of a molecule has a significant impact on its rate of diffusion. Larger molecules, due to their greater mass and likelihood of collisions, diffuse at a slower rate than smaller molecules. This is an important concept to understand in chemistry, as it can affect everything from the rate at which a gas fills a room to the rate at which drugs are absorbed into the body.