Matter in our Surroundings class 9 Notes
Matter in our Surroundings class 9 Notes
Introduction
- Matter is anything that has mass and occupies space.
- Ancient philosophers explained matter using five elements (Panch Tatva): air, earth, fire, sky, and water.
- Modern scientists classify matter based on physical and chemical properties.
Physical Nature of Matter
1. Matter is made up of particles
1) All matter consists of very tiny particles.
2) Particles of matter have space between them.
3) Particles of matter are constantly moving.
4) Particles of matter attract each other.
Example (Diffusion):
- When a drop of ink is put in water, it slowly spreads throughout the water without stirring. This happens because the particles of matter keep moving and mixing.
2. How small are these particles of matter?
- Matter is made up of very tiny particles. These particles are so small that we cannot see them with our naked eyes.
- Scientists proved their small size through different experiments.
1. Experiment with Potassium Permanganate
- Take a small crystal of Potassium Permanganate and dissolve it in water.
- The water becomes purple in color.
- Now take 10 ml of this solution and mix it in 100 ml of fresh water.
- Repeat this process many times.
Observation:
- Even after many dilutions, the water still remains slightly purple.
Conclusion:
- This shows that a single crystal contains millions of extremely tiny particles that spread throughout the water.
2. Example with Perfume or Incense
- When someone sprays perfume or burns incense sticks, the smell spreads throughout the room.
- This happens because the tiny particles of the substance move in air and mix with it.
3. Main Points
- Particles of matter are extremely small in size.
- A small amount of matter contains millions of particles.
- These particles spread and mix easily with other substances.
Characteristics of Particles of Matter
1) Particles of matter have space between them.
2) Particles of matter are continuously moving.
3) Particles of matter attract each other.
States of Matter
- Matter exists in different forms called states of matter.
- The state of matter depends on the arrangement and movement of particles and the force of attraction between them.
- The three main states of matter are solid, liquid, and gas.
1. Solid
Definition:
- A solid is a state of matter in which particles are very closely packed and have strong force of attraction.
Properties
- Solids have a fixed shape and fixed volume.
- Particles are tightly packed.
- Particles cannot move freely; they only vibrate in their fixed positions.
- Solids are hard and rigid.
- They do not flow.
Examples
- Stone
- Wood
- Ice
- Iron
2. Liquid
Definition:
- A liquid is a state of matter in which particles are less tightly packed than in solids.
Properties
- Liquids have a fixed volume but no fixed shape.
- They take the shape of the container.
- Particles can move and slide past each other.
- Liquids flow easily.
- Force of attraction is weaker than solids but stronger than gases.
Examples
- Water
- Milk
- Oil
- Juice
3. Gas
Definition:
- A gas is a state of matter in which particles are very far apart and have very weak force of attraction.
Properties
- Gases have no fixed shape and no fixed volume.
- They fill the entire container.
- Particles move very freely and very fast.
- Gases are highly compressible.
- They spread quickly in all directions.
Examples
- Air
- Oxygen
- Carbon dioxide
Can Matter Change Its State?
- Yes, matter can change its state from solid to liquid to gas and vice-versa.
- This change happens mainly due to change in temperature or change in pressure.
- When temperature or pressure changes, the energy of particles and the distance between them change.
1. Effect of Change of Temperature
- When the temperature increases, the kinetic energy of particles increases.
- Because of this, particles move faster and the force of attraction between them decreases, which changes the state of matter.
(a) Melting (Solid → Liquid)
- The process in which a solid changes into liquid on heating is called melting.
- Example: Ice changes into water at 0°C.
(b) Boiling or Vaporisation (Liquid → Gas)
- The process in which a liquid changes into gas on heating is called boiling or vaporisation.
- Example: Water changes into steam at 100°C.
(c) Freezing (Liquid → Solid)
- When the temperature decreases, a liquid changes into solid. This process is called freezing.
- Example: Water changes into ice.
(d) Condensation (Gas → Liquid)
- The process in which gas changes into liquid on cooling is called condensation.
- Example: Water vapour changes into water droplets.
2. Effect of Change of Pressure
- Changing pressure can also change the state of matter, especially in gases.
- When pressure is increased, gas particles come closer together and may change into liquid.
- When pressure is decreased, particles move farther apart.
- Example: Petroleum gas used for cooking is stored as liquid in cylinders under high pressure. Liquefied Petroleum Gas is stored in cylinders by compressing the gas, which converts it into liquid.
Evaporation
- Evaporation is the process in which a liquid changes into vapour at any temperature below its boiling point.
- It takes place only at the surface of the liquid.
Example:
- Drying of wet clothes
- Sweat drying from our body
- Water slowly disappearing from an open vessel
Factors Affecting Evaporation
- The rate of evaporation depends on several factors:
1) Surface Area
- If the surface area increases, the rate of evaporation also increases because more particles can escape from the surface.
- Example: Wet clothes dry faster when they are spread out.
2) Temperature
- When temperature increases, the rate of evaporation increases because particles get more kinetic energy and escape easily into the air.
- Example: Clothes dry faster on a hot sunny day.
3) Humidity
- Humidity means the amount of water vapour present in the air.
- If humidity is high, evaporation is slow.
- If humidity is low, evaporation is fast.
- Example: Clothes dry slowly during the rainy season because the air already contains a lot of water vapour.
4) Wind Speed
- If wind speed increases, evaporation increases because wind removes the water vapour near the surface.
- Example: Clothes dry faster on a windy day.
How Does Evaporation Cause Cooling?
- During evaporation, particles of liquid absorb heat energy from the surroundings to change into vapour.
- The particles with higher energy escape first from the liquid surface.
- The remaining particles have lower energy, so the temperature of the liquid decreases.
- This causes cooling of the surface.
Examples
- When sweat evaporates from our skin, it removes heat from the body and makes us feel cool.
- Water kept in an earthen pot becomes cool due to evaporation through tiny pores.
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