Diffusion is the spreading out of particles, moving from an area of high concentration to one of low concentration.

Diffusion in Liquids

Look at the diagram below in which a drop of pink ink is dropped into a beaker of water.

Due to the motion of molecules in water, the ink particles slowly mix with the water. The entire process illustrates diffusion between the pink ink particles and the water particles.

Ink Diffusion Steps

1. When the ink is dropped in the beaker, the ink particles are bundled together at the top right. This means that there is a high concentration of ink at the top right of the beaker. In other words, there’s a high concentration of ink particles in that area of the water.

2. Due to diffusion, the ink particles will spread out from a high concentration to a low concentration. That’s why, in the second beaker, the ink has spread out, although a lower concentration of ink remains on the left and bottom sides.

3. In the third beaker, the ink particles have successfully spread throughout the beaker, which means the ink has been diffused in the water.

For diffusion to occur, there needs to be a difference in concentration, known as a concentration gradient. For example, in the ink example above, the ink particles spread to the areas of the beaker where there was an uneven amount of ink particles relative to the water. The ink particles continue to diffuse if there is a concentration gradient.

Diffusion in Gases

This process is common in gases, allowing substances to mix together. As gas particles are very spread out, they are able to move and vibrate quickly. The gas spreads to sections of the room where its concentration is lower. This occurs until the gas is evenly distributed around the entire room.

For example, a spray of perfume in one corner of the room will diffuse to the other side of the room, which will soon cause the whole room to smell of the perfume.

  • Diffusion is faster in gases than in liquids

Brownian Motion

Brownian motion is the random movement of particles in gases due to collisions.

When particles are free to move around, they collide with other moving particles in the air. This causes particles to follow random paths and spread out in a random fashion.

Factors Affecting the Rate of Diffusion

FactorImpact on the Rate of Diffusion
TemperatureAs the temperature increases, the rate of diffusion also increases. This is because particles have more energy and therefore move faster.
Size of particlesThe smaller the particle, the faster the rate of diffusion
State of MatterDiffusion does not occur in solids, and it is faster in gases than in liquids.