Class 9 | Science
1. Introduction to Matter:
- Matter is anything that occupies space and has mass.
- Matter exists in three physical states: solid, liquid, and gas.
- Interconversion of these states is possible through heating or cooling.
2. Characteristics of Particles in Matter:
- Particles in matter are in constant motion.
- The inter-particle space and forces between particles vary with the state of matter.
- Particles are closely packed in solids, with strong forces of attraction.
- Particles in liquids are less closely packed, with weaker forces.
- Particles in gases are widely separated, with negligible forces.
3. Change of State:
- Melting is the change of a solid into a liquid due to heating.
- Freezing is the change of a liquid into a solid due to cooling.
- Evaporation is the change of a liquid into a gas at any temperature.
- Condensation is the change of a gas into a liquid.
- Sublimation is the change from a solid directly to a gas without passing through the liquid state.
4. Effect of Heat on Matter:
- Heating a substance increases the kinetic energy of its particles.
- The temperature at which a substance changes from a solid to a liquid is its melting point.
- The temperature at which a substance changes from a liquid to a gas is its boiling point.
- Heating curves show the change in temperature as a substance is heated.
5. Factors Affecting Evaporation:
- Surface area: Larger surface area increases evaporation.
- Temperature: Higher temperature leads to faster evaporation.
- Wind speed: Increased wind speed enhances evaporation.
- Humidity: Lower humidity promotes faster evaporation.
6. Evaporation Causes Cooling:
- Evaporation is a cooling process because it takes away heat energy.
- This principle is used in the cooling effect of sweat on the body.
7. Sublimation:
- Sublimation is the process where a substance changes from a solid directly to a gas.
- Examples include the sublimation of dry ice (solid CO2) and naphthalene balls.
8. Diffusion:
- Diffusion is the spontaneous mixing of particles of different substances due to their random motion.
- It is faster in gases, slower in liquids, and very slow in solids.
9. Brownian Motion:
- Brownian motion is the erratic, zigzag movement of small particles suspended in a fluid due to collisions with fast-moving particles.
10. Matter is Composed of Particles:
– The particle nature of matter explains various properties and behaviors of matter in our surroundings.
Multiple choice questions
- What is the process by which a solid changes directly into a gas without passing through the liquid state?
a) Melting
b) Freezing
c) Sublimation
d) Evaporation - In which state of matter do particles have the least amount of kinetic energy?
a) Solid
b) Liquid
c) Gas
d) All have the same amount of kinetic energy - Which of the following is an example of a physical change?
a) Burning of paper
b) Rusting of iron
c) Melting of ice
d) Digestion of food - What is the change of a liquid into a gas at any temperature called?
a) Melting
b) Freezing
c) Evaporation
d) Condensation - What happens to the particles in a substance when it is heated?
a) They slow down
b) They stop moving
c) They move faster
d) They change their state immediately - What is the temperature at which a substance changes from a liquid to a gas called?
a) Freezing point
b) Melting point
c) Boiling point
d) Condensation point - Which of the following has the highest rate of diffusion?
a) Solid
b) Liquid
c) Gas
d) All have the same rate of diffusion - What happens to the particles during the process of diffusion?
a) They move closer together
b) They become more ordered
c) They spread out and mix with other particles
d) They remain stationary - Which of the following substances undergoes sublimation?
a) Water
b) Salt
c) Dry ice (solid CO2)
d) Sugar - Which factor does NOT affect the rate of evaporation?
a) Surface area
b) Temperature
c) Wind speed
d) Volume of the liquid - What is the cooling effect of a liquid as it changes to a gas during evaporation called?
a) Melting
b) Boiling
c) Sublimation
d) Latent heat of vaporization - What causes the Brownian motion of particles in a fluid?
a) Gravity
b) Magnetic fields
c) Random collisions with fast-moving particles
d) Static electricity - Which state of matter has the least inter-particle spacing and the strongest forces of attraction between particles?
a) Solid
b) Liquid
c) Gas
d) Plasma - What is the process of a gas changing into a liquid called?
a) Sublimation
b) Evaporation
c) Condensation
d) Fusion - Which of the following substances does NOT exist in all three states of matter (solid, liquid, gas) under normal conditions?
a) Water
b) Oxygen
c) Gold
d) Carbon dioxide - What is the term for the temperature at which a solid changes into a liquid?
a) Boiling point
b) Freezing point
c) Melting point
d) Condensation point - Which of the following factors does NOT affect the rate of diffusion?
a) Temperature
b) Size and mass of particles
c) Presence of other substances
d) Pressure - What happens to the volume of a gas when it is cooled at constant pressure?
a) It increases
b) It decreases
c) It remains the same
d) It depends on the gas - Which substance is an example of a chemical change?
a) Ice melting into water
b) Iron rusting
c) Water evaporating
d) Salt dissolving in water - What type of change occurs when a liquid changes into a solid?
a) Chemical change
b) Physical change
c) Nuclear change
d) Thermal change
Key
Certainly, here are the answers to the multiple-choice questions:
- c) Sublimation
- a) Solid
- c) Melting of ice
- c) Evaporation
- c) They move faster
- c) Boiling point
- c) Gas
- c) They spread out and mix with other particles
- c) Dry ice (solid CO2)
- d) Volume of the liquid
- d) Latent heat of vaporization
- c) Random collisions with fast-moving particles
- a) Solid
- c) Condensation
- b) Oxygen
- c) Melting point
- d) Pressure
- b) It decreases
- b) Iron rusting
- b) Physical change