Class 9 Science

Diffusion of Matter

The phenomenon of mixing of particles of different substances together is known as diffusion. Diffusion takes place because of the movement of particles of matters.

Diffusion comes from Latin word diffundere which means to spread out. Diffusion is a natural process. The mixing of different gases in air is a natural process that continuously takes place. Diffusion takes place in all states of matter, i.e. solid, liquid and gases.

Diffusion takes place from higher concentration to lower concentration. This means that particles of a particular matter move from its area of higher concentration to that of lower concentration.

When a person presses the nozzle of a perfume bottle, some gases come out of the nozzle. These gases move away from the nozzle because they tend to move from area of higher concentration to that of lower concentration. Due to this, the fragrance of perfume spreads far and wide.

It was Robert Brown who discovered the random movement of particles of matter. Albert Einstein developed the theory of Brownian motion based on the discovery of Robert Brown.

Diffusion in gas

Diffusion takes place most rapidly in gases.It is possible because of very high kinetic energy possessed by particles of gases. Particles of gases move at high speed because of high kinetic energy.

Example: Smoke coming out of factories is seen only near the mouth of chimneys. After rising high it mixes up with air and vanishes out. This happens because of diffusion of gases.

Diffusion in liquid

The rate of diffusion is less in liquid than that of gases. The particles of liquid have enough movement because of kinetic energy for diffusion. When two liquids are kept together they get mixed because of diffusion.

Example: When salt solution is kept in water this makes the whole solution salty after some time. This happens because of diffusion in liquids. Similarly, when you pour rose syrup in a drink, the drink becomes sweet because of diffusion of rose syrup in the drink.

Diffusion in solid

Diffusion takes place at the slowest rate in the case of solids. The rate of diffusion is almost negligible in solids. This happens because particles of solid have the lowest kinetic energy. It takes pretty long time for a matter to diffuse in solid.

Example: You may have observed that the chalk mark on black board becomes difficult to remove, after a certain time. This happens because of the diffusion of particles of chalks with the particles of black-board.

Alloys are mixtures of two or more than two metals or a metal and a non-metal. Production of alloys is possible because of diffusion of solid into solid. Bronze, steel, brass are the examples of alloy.

Diffusion in everyday life

Aroma from Food

What happens when your mother is cooking your favourite dish in the kitchen? You get the aroma of food while sitting in your study room. The aroma cmoes to your nostrils because of diffusion of certain particles from the kitchen. These particles carry the aroma to you.

Fragrance from Incense Stick

When an incense stick is burnt in the sacred corner of your house, the whole house gets the fragrance. It happens because the vapor from the incense stick diffuse in air in every part of the house.

It is because of diffusion that you get obnoxious smell from heap of garbage across the road.

Dissolution in Water

When sugar is added in water, it gets mixed with water because of diffusion. The particles of sugar collide with the particles of water because of their continuous movement. And finally they are mixed together because of diffusion.

Carbonated drinks are prepared by diffusion of gas in water. We notice a hiss sound when the cap of a bottle of carbonated drink is opened. The hissing sound comes because of the diffused gas coming out of water. Soda, Soft drinks (coca-cola) etc. are carbonated drinks and prepared by mixing carbon dioxide in water.

Aquatic animals breathe in oxygen that remains dissolved in water. In your biology lessons, you have read that plants need carbon dioxide for photosynthesis. How do aquatic plants get carbon dioxide? They get carbon dioxide which remains dissolved in water. These gases dissolve in water because of the diffusion.

Temperature and Rate of Diffusion

The rate of diffusion increases with increase in temperature and decreases with decrease in temperature.

Diffusion takes place because of the movements of particles of matters. An increase in temperature increases the kinetic energy of particles. This increases the speed of movement of particles of matter. As a result, the rate of diffusion increases.

Example: We do not get the smell of cold food from a distance, but we get the smell of hot food even from a distance. Hot food has higher temperature. Higher temperature increases the kinetic energy of particles and hence the aroma of hot food easily travels far and wide. That is why, you will not get the aroma of ice-cream but you will always get the aroma of piping hot jalebis and samosa from a distance.