Page 8 - CLASS VII Lesson Notes Forces and Energy

SUBTOPIC: 3.7 PARTICLES ON THE MOVE

Key Words:
diffusion, concentration

What Is Diffusion?
• Diffusion is the spreading out of particles from an
area of high concentration to an area of low
concentration.
• It happens because particles are always moving
randomly.

Diffusion in Gases:
• Particles in a gas move quickly and randomly in all directions.
• When two gases are mixed, the particles spread out and fill the
space through diffusion.
• Example: Smelling food or perfume across a room happens
because gas particles spread through the air.

Diffusion in Liquids:
• Particles in a liquid also move randomly, though more slowly than
in gases.
• When a liquid like ink is added to water, the ink spreads out
through the water by diffusion.

What Affects the Speed of Diffusion?
1. Concentration Difference:
A bigger difference in concentration makes diffusion happen faster.
2. Temperature Difference:
Higher temperature = particles move faster = faster diffusion.
Example:
Tea spreads faster in hot water than in
cold water.

Important Points:
• Diffusion stops when the
concentration becomes equal
throughout the space.
• Even after diffusion is complete,
particles keep moving — they just
move evenly in all directions.

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