CBSE NCERT Science Class 9 Chapter 1: Matter in Our Surroundings

Chapter 1: Matter in Our Surroundings

Notes:

1. Matter: 

- Everything around us is made up of matter. Matter is anything that has mass and occupies space.

- It can be classified into three states: solid, liquid, and gas, based on the arrangement and movement of particles.

2. Characteristics of Particles of Matter:

- Particles of matter are very small and are constantly moving.

- They have spaces between them, and these spaces increase on heating.

- The particles attract each other, and the force of attraction is maximum in solids and minimum in gases.

3. States of Matter:

a. Solid:

- Solids have a definite shape and volume.

- The particles are closely packed in an orderly manner.

- They have fixed positions and vibrate around their mean positions.

- Solids cannot be compressed much.

b. Liquid:

- Liquids have a definite volume but no fixed shape.

- The particles in liquids are closely packed but can move around each other.

- They can flow and take the shape of the container they are poured into.

- Liquids cannot be compressed significantly.

c. Gas:

- Gases have neither a definite shape nor a definite volume.

- The particles in gases are widely spaced and move randomly at high speeds.

- They can expand to fill the entire available space and can be compressed easily.

4. Can Matter Change Its State?

- Yes, matter can change its state through heating or cooling.

- The process of changing a solid into a liquid is called melting, and the reverse is called freezing.

- The process of changing a liquid into a gas is called evaporation, and the reverse is called condensation.

- The process of changing a solid directly into a gas without melting is called sublimation.

5. Evaporation:

- Evaporation is the process by which a liquid changes into a gas at its surface, even below its boiling point.

- Factors affecting the rate of evaporation include temperature, surface area, and wind speed.

6. Cooling Effect of Evaporation:

- During evaporation, the particles with higher energy evaporate, leaving behind the particles with lower energy.

- This leads to a decrease in the average kinetic energy and temperature of the liquid, resulting in a cooling effect.

7. Condensation:

- Condensation is the process by which a gas changes into a liquid on cooling.

- It is the reverse of evaporation.

8. Sublimation:

- Sublimation is the process of changing a solid directly into a gas without melting.

- Substances that undergo sublimation are called sublime.

9. Effect of Change of Pressure:

- An increase in pressure can convert a gas into a liquid or a solid, whereas a decrease in pressure can convert a solid into a gas directly.

10. Effect of Change of Temperature:

- Increasing the temperature generally leads to an increase in kinetic energy, resulting in a change of state from solid to liquid to gas.

- Decreasing the temperature leads to a decrease in kinetic energy, causing a reverse change of state.

11. Latent Heat:

- Latent heat is the heat energy absorbed or released during a change of state without any change in temperature.

- The latent heat of fusion is the heat absorbed during the change of a solid to a liquid at its melting point.

- The latent heat of vaporization is the heat absorbed during the change of a liquid to a gas at its boiling point.

12. Evaporation and Cooling:

- The cooling effect of evaporation is used in various cooling systems like air conditioners, desert coolers, and refrigerators.

These are the key points covered in the chapter "Matter in Our Surroundings" of the NCERT Science textbook for Class 9.