Class 9 Science Chapter 1 Important Extra Questions

The properties of particles of matter are:
(i) The particles of particles matter attract to each other.
(ii) The particle of matter continuously moving.
(iii) The particle of matter has space between them.

Anything that has mass and volume and made up of very small particle is called matter.

(i) Mass = 1kg
(ii) Volume = m³
(iii) Temperature= kelvin
(iv) Work = Joule
(v) Density = (mass )/volume = kgm⁻³

The intermixing of particle of two different types of matter on their own is called diffusion. The rate of diffusion increases on increasing the temperature of diffusing substance. Diffusion is a natural process. It takes place in solid, liquid and gas.

The process of melting of solid and it will become change into liquid is known as fusion.

(a) Particles of matter attract each other because of force of attraction:
(i) The force of attraction between particle of matter keep the particles bonded together. The force of attraction between particles of solid is greatest, between particles of liquid is moderate and between particles of gas is lowest.
(ii) Because of the lowest force of attraction between particles of gas we can move our hand through air easily. To move our hand in water we have to apply some force, but from a solid such as wood, we cannot move our hand.
(iii) This is because the force of attraction between particles of gas is almost negligible, in liquid the force of attraction is moderate but is greatest in solid.
(iv) The force of attraction between particle of solid, liquid and gas can be arranged in decreasing order as follows solid, liquid and gas.
(a) Particles of matter have space between them:
(i) Gas can be compressed a lot because of the space between their particles.
(ii) When sugar is dissolved in water the particle of sugar disappears in water. This happen because particles of sugar get adjusted in the space between particles of water. Additionally, you will notice that there is no rise of water level take place when one or teaspoon of sugar is added in a glass of water and this is because particles get adjusted in the space between the particle of water and no rise in the water level comes in result.

The minimum temperature at which solid start melting to become a liquid at the atmospheric pressure is called melting point of solid. The melting point of ice is 273.13K.

The temperature at which a liquid starts boiling at the atmospheric pressure is known as boiling point. It’s boiling point is 100C or 373K.

The heat energy required to convert 1 kilogram of a solid into liquid at atmospheric pressure at its melting point. This is known as the latent heat of fusion.

The particles in the steam have observed extra energy and their energy is called the latent heat of fusion.

The process of changing of solid directly into gases state without changing into liquid, state or vice versa is known as sublimation.

Yes all material possess mass and occupy space.

This observation indicates that particles of water have space between them into which sugar particles fit.

The balloon burst and diffusion takes place.

When Dettol is added to water, diffusion take place.

(i) Liquid
(ii) Gas

(i) Liquid state
(ii) Gaseous state

Density of a substance is defined as the mass per unit volume. Its SI unit kgm⁻³.

NaCl has particles with the highest forces of attraction.

When we place few crystals of potassium permanganate in a beaker containing water we get two distinct layers colourless water at the top and pink colour at the bottom. After few minutes, pink colour spreads and whole solution turns pink due to diffusion. Since potassium permanganate is a solid substance, it does not possess so much space. Water molecules due to liquid states, collide with solid particles and intermixes due to sufficient space between molecules.

In solid the particles have highly ordered arrangement because the intermolecular forces between the particles are very strong. Therefore, solids have a regular geometrical shape.

Gases are compressibility because the intermolecular space is very large in areas, whereas liquids are not compressibility because in liquids the intermolecular space is less.

Yes, rubber band change shape under force and regains the same shape when the force is removed. It breaks on applying excessive force. Yes it is a solid.

Steam at 1000 ⁰C better for heating purposes than water at 1000 ⁰C because the energy of 1 kg of steam at 1000 ⁰C is 22.6 × 10⁵ joule which is more than that of 1kg of water at the same temperature.

(a) To check whether the substance is pure or not.
(b) To identify the characteristic the substance.

The temperature of both boiling water and steam 1000C but steam has more energy because latent heat of vaporisation.

The temperature of a substance remains constant at its melting and boiling points until all the substance melts or boils because, the heat supplied is continuously used up in changing the state of substance by overcoming the forces of attraction between the particles. This heat energy absorbed without showing any rise in temperature is given the name latent heat of fusion/latent heat of vapourisation.

The amount of heat that is required to change 1kg of solid into liquid at atmospheric pressure without any change in temperature at its melting point, is known as latent heat of fusion. The latent heat of fusion of ice in SI unit is 3.35 × 10⁵ J/kg.

Solid CO2 is known as dry ice. This is because is directly gets converted into gaseous state without passing through liquid state on decreasing the pressure to 1 atmosphere.

When a person has fever his body temperature becomes more than the normal body temperature. If we put strips of wet cloth on the forehead of a person suffering from high fever, the water evaporates taking heat from the body. Thus moist strips will lower his body temperature.

The temperature in the sunny area is higher than in the shade and evaporation take place at a faster rate at high temperature. Hence wet clothes dry quickly in the sun.

During summer the temperature is generally very high. In order to keep cool a tree must transpire (transpiration is a phenomena of evaporation of water from the leaves) more to keep itself cool. More transpiration requires more leaves. Hence a tree acquires more leaves during summer.

The sweat is readily evaporated from the body by the air from the fan. As a result, we feel comfortable under a fan.

Water sprinkled on the roof evaporates by taking the large latent heat of vaporisation from the ground. This makes the place cool and comfortable.

Priyanshi would be more comfortable because cotton is a good absorber than nylon. It absorbs sweat from the body and provides large surface area for evaporation which causes cooling effect. As a result, body feels cool and comfortable.

A is a gas. Properties of gases are as follows:
(i) They do not have fixed shape and fixed volume.
(ii) They have large inter-particle space.
(iii) They have least forces of attraction between the molecules.
(iv) They are highly compressibility.

(i) Molecular motion decreases as water gets converted into ice.
(ii) Latent heat of solidification is given off.
Latent heat of solidification is equal to latent heat of fusion.

Conditions that can increases the rate of evaporation of water are:
(a) An increases in the surface area by spreading the shirt.
(b) An increases in the temperature by putting the shirt under the sun.
(c) Increases in the wind speed by spreading it under the fan.

(a) To demonstrate motion of particles in air:
(i) Place few lighted incense sticks in a corner of a room.
(ii) Move about the room and smell the fragrance of the incense sticks.
The fragrance produce produced due to burning of incense sticks is due to movement of vapours produce rapidly in all direction.
(b) To demonstrate motion of particle of solid matter:
(i) Drop a crystal of copper sulphate or potassium permanganate into a glass of hot water.
(ii) Do not stir the solution and allow the crystals to settle at the bottom.
(iii) The colour of the solid is seen spreading slowly. This is because the solid particles diffuse in the water.

Factors affecting the rate of evaporation:
(a) Surface area: The rate of evaporation increases with increase in surface area.
(b) Temperature: The rate of evaporation increases with increases in temperature.
(c) Humidity: The rate of evaporation decreases with increases in humidity.
(d) Wind Speed: The rate of evaporation increases with increases in wind speed.
(e) Nature of the liquid: The volatile compounds evaporate faster than less volatile compounds.
B will produce more cooling effect because it will absorb more heat from the surrounding for evaporation.

The particles of hot sizzling food get temperature and their kinetic energy increases so they move fast and mix up in the air and the smell reaches us while the temperature of particles of cold food is low so the particles of cold food is low so the particles do not move fast and they do not mix up in the air and reaches soon.

Evaporation produces cooling aa the particles at the surface of the liquid grain energy from the surroundings and change into vapour thereby producing a cooling effect.

Air around us cannot hold more than a definite amount of water vapour at a given temperature which is known as humidity. So if the air is already rich in water vapour, it will not take up more water therefore rate of evaporation of water will decrease.

A sponge has minutes’ holes in which air is trapped. Also the material is not rigid. When we press it the air is expelled out and we are able to compress it. But it is solid because it has definite shape and volume and does not change its shape unless compress.

Ice is solid at O degree Celcious because it has a definite volume and definite shape due to strong intermolecular force shape due to weak intermolecular force of attraction.