Diffusion

1. Diffusion is a fundamental process that demonstrates the random motion and mixing of particles in liquids and gases.
2. It is defined as the movement of particles from a region of higher concentration to a region of lower concentration, driven by their intrinsic kinetic energy.
3. This process, explained by the kinetic particle theory, is a key concept in understanding the dynamic behaviour of matter.

How Diffusion Works

1. Diffusion occurs due to the constant, random motion of particles.
2. As particles move and collide with each other, they spread out to occupy available space evenly.
3. The process is spontaneous and requires no external force.
4. For example:
   Imagine dropping a dye tablet into a glass of water. The dye molecules, initially concentrated in one spot, gradually spread throughout the water, eventually resulting in a uniformly coloured solution. This is a visual demonstration of diffusion.

Experimental Examples of Diffusion

1. Dissolving Potassium Manganate(VII) in Water:
   When purple crystals of potassium manganate(VII) are added to water, the purple colour spreads throughout without stirring. This is due to the random motion of potassium manganate(VII) particles colliding with water molecules and spreading evenly.
2. Mixing Gases:
   A classic experiment involves placing a jar of air on top of a jar of bromine gas. Over time, the bromine gas (heavier than air) mixes completely with the air, demonstrating that gas particles diffuse freely due to their random motion.
3. Hydrogen and Air Mixing:
   In another experiment, hydrogen (a very light gas) and air mix uniformly despite their density difference. This supports the idea that diffusion is driven by random particle motion rather than gravity.

Factors Influencing the Rate of Diffusion

1. Temperature:
   Higher temperatures increase the kinetic energy of particles, leading to faster movement, more frequent collisions, and a quicker rate of diffusion.
2. Relative Molecular Mass:
   Lighter particles move faster at a given temperature, resulting in a higher diffusion rate. For example, hydrogen diffuses much faster than carbon dioxide due to its lower molecular mass.
3. State of Matter:
   Diffusion is fastest in gases, where particles are far apart and experience minimal intermolecular forces. It is slower in liquids due to stronger attractive forces and negligible in solids, where particles are fixed in position.

Significance of Diffusion

1. The process of diffusion provides strong evidence for the kinetic particle theory.
2. The random motion and spreading of particles observed in both liquids and gases support the theory’s claim that matter consists of particles in constant, random motion.
3. This phenomenon highlights the dynamic nature of matter and reinforces our understanding of particle behaviour.