Chapter 1 ยท ICSE Class 8 Chemistry (Selina Concise)

Matter

Deepen your understanding of matter's particle nature and kinetic theory explaining changes of state.

โš›๏ธ Chapter 1

The cycle of changes between solid, liquid, and gas states of matter A triangular cycle showing solid changing to liquid by melting, liquid to gas by boiling, gas back to liquid by condensing, and liquid back to solid by freezing Solid Liquid Gas melting โ†’ โ† freezing boiling โ†’ โ† condensing
1.1

Kinetic Theory of Matter

The kinetic theory states that particles of matter are always in motion, and this motion increases with temperature.

1

Why does increasing temperature increase the rate of diffusion of a gas?

Higher temperature gives particles more kinetic energy, so they move faster and spread out (diffuse) more quickly

2

Why do solids have less particle movement than gases?

Solid particles are held by strong forces and can only vibrate in place, while gas particles have enough energy to move freely

1.2

Diffusion

Diffusion is the movement of particles from an area of high concentration to low concentration, occurring naturally due to particle motion.

1

Why can you smell perfume across a room even without air currents?

Perfume particles diffuse through the air, spreading from high to low concentration due to their constant random motion

2

Does diffusion happen faster in gases or liquids?

Gases, since gas particles move faster and have more space to move through

Practice

Exercises

1. What does the kinetic theory of matter state?

2. What is diffusion?

3. Why does diffusion happen faster at higher temperatures?

4. Does diffusion happen faster in gases or solids?

5. Give an example of diffusion in daily life.