Diffusion is the spreading out of particles. Moving from a high concentration to a low concentration.

Diffusion in Liquids

Look at the diagram below in which a drop of pink ink is dropped into a beaker of water. Because of the motion of molecules in water, the ink particles slowly mix with the water. The overall process is 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. Or in other words, there are a lot of ink particles per volume of water.

2. Due to diffusion, the ink particles will spread out from a high concentration to a low concentration. This is why in the second beaker, the ink has spread out but there is still a low concentration of ink on the left and bottom of the beaker.

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 take place, there needs to be a difference in concentration, which is called 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 tends to happen in gases, allowing substances to mix together. As gas particles are very spread out, they are able to move and vibrate quickly. The gas moves to a section of a room where there is a lower concentration of it. 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 motion of gases due to collision.

When particles are free to move around, they collide with other moving particles in the air. This makes particles take a random path 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 increases – The particles have more energy so they will be moving faster
Size of particlesThe smaller the particle, the higher the rate of diffusion
State of MatterDiffusion does not take place in solids and diffusion is faster in gases than in liquids