Diffusion

Objective: Describe and explain diffusion in terms of kinetic particle theory

What is Diffusion?

Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration. This movement continues until the particles are evenly distributed throughout the available space.

Kinetic Particle Theory and Diffusion

The kinetic particle theory provides a microscopic explanation for diffusion. This theory states that:

• All matter is made up of particles in constant random motion.
• The average kinetic energy of particles is directly proportional to the absolute temperature (in Kelvin).
• The mass of the particles is negligible compared to the distances between them.
• Collisions between particles are perfectly elastic.

Here's how the kinetic particle theory explains diffusion:

1. Particles in a region of high concentration have a greater number of particles colliding with the surrounding particles.
2. These collisions cause the particles to move randomly in all directions.
3. Due to the constant random motion, particles from the high concentration region will move into the lower concentration region.
4. This net movement of particles from high to low concentration is what we observe as diffusion.

Factors Affecting Diffusion Rate

The rate of diffusion is affected by several factors:

• Concentration Gradient: The steeper the concentration gradient (the greater the difference in concentration), the faster the rate of diffusion.
• Temperature: Higher temperatures increase the average kinetic energy of the particles, leading to faster movement and a quicker rate of diffusion.
• Size of Particles: Smaller particles diffuse faster than larger particles because they experience fewer collisions and can move more easily.
• Medium: Diffusion occurs faster in gases than in liquids, and faster in liquids than in solids. This is because particles are more widely spaced in gases and liquids, resulting in fewer collisions.

Table Summarizing Factors Affecting Diffusion

Factor	Effect on Diffusion Rate
Concentration Gradient	Steeper gradient = Faster diffusion
Temperature	Higher temperature = Faster diffusion
Size of Particles	Smaller particles = Faster diffusion
Medium	Gas > Liquid > Solid

Example: Diffusion of Gases

Consider the diffusion of a gas like oxygen from an area of high concentration (e.g., near the lungs) to an area of low concentration (e.g., in the blood). The oxygen molecules are in constant random motion due to their kinetic energy. They collide with each other and with the molecules in the blood, causing them to spread out until the concentration of oxygen is uniform throughout the blood.