Class 9 Matter, States of matter and evaporation

Topics to be covered

`=>` Matter
`=>` States of matter
`=>` Can matter change its state?
`=>` Effect of change of pressure
`=>` Evaporation


Anything which occupies space and has mass is called matter. For eg:chair,car,table, clouds, stars etc.

`color{green}("๐’๐Ž๐Œ๐„ ๐ˆ๐Œ๐๐Ž๐‘๐“๐€๐๐“ ๐€๐‚๐“๐ˆ๐•๐ˆ๐“๐ˆ๐„๐’")`


`color{green}(โ€ข)` Matter is made up of tiny particles.

`color{green}(โ€ข)` There is space between tiny particles.

`color{green}(โ€ข)` Particles of matter are very small.


`color{green}(โ€ข)` Particles of matter are continuously moving, that is, they possess what we call the kinetic energy.

`color{green}(โ€ข)` As the temperature rises, particles move faster. So, we can say that with increase in temperature the kinetic energy of the particles also increases.

`color{green}(โ€ข)` Particles of matter intermix on their own with each other. They do so by getting into the spaces between the particles.

This intermixing of particles of two different types of matter on their own is called `color{red}("๐๐ข๐Ÿ๐Ÿ๐ฎ๐ฌ๐ข๐จ๐ง")` and on heating,
diffusion becomes faster.

`color{green}("๐๐‘๐Ž๐๐„๐‘๐“๐ˆ๐„๐’ ๐Ž๐… ๐Œ๐€๐“๐“๐„๐‘")`

`color{green}(โ€ข)` Matter is made up of small particles.

`color{green}(โ€ข)` These particles are very small in size.

`color{green}(โ€ข)` These particles are moving constantly( They possess what we call the kinetic energy. As the temperature rises, particles move faster. So, we can say that with increase in temperature the kinetic energy of the particles also increases.)

`color{green}(โ€ข)` These particles have spaces between them.

`color{green}(โ€ข)` Particles of matter attract each other because of force of attraction present between them.

States of matter

Matter around us exists in three different statesโ€“ solid, liquid and gas. These states of matter arise due to the variation in the characteristics of the particles of matter.


`color{green}(โ€ข)` They have fixed volume and shape.

`color{green}(โ€ข)` Particles are closely packed .

`color{green}(โ€ข)` They have less spacing between them.

`color{green}(โ€ข)` They have distinct boundaries.

`color{green}(โ€ข)` They have negligible compressibility.

`color{green}(โ€ข)` They are rigid.

`color{green}(โ€ข)` Example: sugar, stone, wood etc.


`color{green}(โ€ข)` They donโ€™t have fixed shape.

`color{green}(โ€ข)` They take the shape of container in which they are kept.

`color{green}(โ€ข)` They have fixed volume.

`color{green}(โ€ข)` They are not rigid.

`color{green}(โ€ข)` They have tendency to flow thatโ€™s why they are called fluids.

`color{green}(โ€ข)` Example: milk, water, petrol etc.


`color{green}(โ€ข)` They have indefinite shape and volume.

`color{green}(โ€ข)` Particles have very large space between them and weak force of attraction.

`color{green}(โ€ข)` Due to high speed of particles and large space between them, gases show the property of diffusing very fast into other gases.

`color{green}(โ€ข)` They are highly compressible.

`color{green}(โ€ข)` Gases can move randomly due to which the particles hit each other and also the walls of the container. The pressure exerted by the gas is because of this force exerted by gas particles per unit area on the walls of the container.

Can Matter Change its State?

`color{green}(โ€ข)` As the temperature of the solids is increased, their kinetic energy increases due to which the particles start vibrating with greater speed. The energy supplied by heat overcomes the forces of attraction between the particles. The particles leave their fixed positions and start moving more freely.

`color{green}(โ€ข)` A stage is reached when the solid melts and is converted to a liquid.

`color{green}(โ€ข)` The temperature at which a solid melts to become a liquid at the atmospheric pressure is called its `color{red}("๐ฆ๐ž๐ฅ๐ญ๐ข๐ง๐  ๐ฉ๐จ๐ข๐ง๐ญ")` . The melting point of ice is `color{red}("273.16 K*")`.

`color{green}(โ€ข)` The process of melting, that is, change of solid state into liquid state is also known as fusion.

`color{green}("๐‹๐€๐“๐„๐๐“ ๐‡๐„๐€๐“ ๐Ž๐… ๐…๐”๐’๐ˆ๐Ž๐")`

During melting, the temperature of the system does not change after the melting point is reached, till all the ice melts. This happens even though we continue to heat the beaker and heat gets used up in changing the state by overcoming the forces of attraction between the particles.

As this heat energy is absorbed by ice without showing any rise in temperature, it is considered that it gets hidden into the contents of the beaker and is known as the `color{red}("๐ฅ๐š๐ญ๐ž๐ง๐ญ ๐ก๐ž๐š๐ญ")`. The word latent means hidden.

The amount of heat energy that is required to change 1 kg of a solid into liquid at atmospheric pressure at its melting point is known as the `color{red}("๐ฅ๐š๐ญ๐ž๐ง๐ญ ๐ก๐ž๐š๐ญ ๐จ๐Ÿ ๐Ÿ๐ฎ๐ฌ๐ข๐จ๐ง")`. So, particles in water at `color{red}(0^0 C (273 K))` have more energy as compared to particles in ice at the same temperature.

`color{green}("๐๐Ž๐ˆ๐‹๐ˆ๐๐† ๐๐Ž๐ˆ๐๐“")`

When we supply heat energy to water, particles start moving even faster. At a certain temperature, a point is reached when the particles have enough energy to break free from the forces of attraction of each other. At this temperature the liquid starts changing into gas.

The temperature at which a liquid starts boiling at the atmospheric pressure is known as its `color{red}("๐›๐จ๐ข๐ฅ๐ข๐ง๐  ๐ฉ๐จ๐ข๐ง๐ญ.")` Boiling is a bulk phenomenon. Particles from the bulk of the liquid gain enough energy to change into the vapour state. For water this temperature is `color{red}(373 K (100^0C = 273 + 100 = 373 K))`. Particles in steam, that is, water vapour at `color{red}(373 K (100^0 C))` have more energy than water at the same temperature. This is because particles in steam have absorbed extra energy in the form of latent heat of vaporisation.

Substances around us change state from solid to liquid and from liquid to gas on application of heat. But there are some that change directly from solid state to gaseous state and vice versa without changing into the liquid state.

A change of state directly from solid to gas without changing into liquid state (or vice versa) is called `color{red}("๐ฌ๐ฎ๐›๐ฅ๐ข๐ฆ๐š๐ญ๐ข๐จ๐ง.")`

`color{red}("Solid State" underset("Cool") overset("Heat")โ‡„ " Liquid State" underset("Cool") overset(" Heat") โ‡„ " Gaseous State")`


When the pressure over the piston is applied the gas present inside the container starts compressing and the particles start coming close to each other. Now when the pressure is applied and temperature is reduced the gases start to liquify.

Solid carbon dioxide `color{red}((CO_2))` is stored under high pressure. It gets converted directly to gaseous state on decrease of pressure to 1 atmosphere* without coming into liquid state. This is the reason that solid carbon dioxide is also known as dry ice.

๐“๐ก๐ฎ๐ฌ, ๐ฐ๐ž ๐œ๐š๐ง ๐ฌ๐š๐ฒ ๐ญ๐ก๐š๐ญ ๐ฉ๐ซ๐ž๐ฌ๐ฌ๐ฎ๐ซ๐ž ๐š๐ง๐ ๐ญ๐ž๐ฆ๐ฉ๐ž๐ซ๐š๐ญ๐ฎ๐ซ๐ž ๐๐ž๐ญ๐ž๐ซ๐ฆ๐ข๐ง๐ž ๐ญ๐ก๐ž ๐ฌ๐ญ๐š๐ญ๐ž ๐จ๐Ÿ ๐š ๐ฌ๐ฎ๐›๐ฌ๐ญ๐š๐ง๐œ๐ž, ๐ฐ๐ก๐ž๐ญ๐ก๐ž๐ซ ๐ข๐ญ ๐ฐ๐ข๐ฅ๐ฅ ๐›๐ž ๐ฌ๐จ๐ฅ๐ข๐, ๐ฅ๐ข๐ช๐ฎ๐ข๐ ๐จ๐ซ ๐ ๐š๐ฌ.


`color{green}(โ€ข)` The process of conversion of liquid to gas due to escaping of particles from liquid surface is called evaporation.

`color{green}(โ€ข)` It takes place only at the surface of liquid.

`color{green}(โ€ข)` It can take place at room temperature also.

`color{green}("๐…๐€๐‚๐“๐Ž๐‘๐’ ๐€๐…๐…๐„๐‚๐“๐ˆ๐๐† ๐‘๐€๐“๐„ ๐Ž๐… ๐„๐•๐€๐๐Ž๐‘๐€๐“๐ˆ๐Ž๐:")`

`color{red}("๐Ÿ ๐’๐”๐‘๐…๐€๐‚๐„ ๐€๐‘๐„๐€")`
Evaporation being the surface phenomena increases with increase in surface area.For eg: wet clothes are spread out so that with increase in surface area evaporation takes place faster and clothes become dry up quickly.

`color{red}("๐Ÿ ๐“๐„๐Œ๐๐„๐‘๐€๐“๐”๐‘๐„")`
Evaporation increases with increase in temperature. This is because as the temperature is increased the particles present at the surface get the required kinetic energy so that they can overcome the force of attraction and escape quickly in air

`color{red}("๐Ÿ‘ ๐‡๐”๐Œ๐ˆ๐ƒ๐ˆ๐“๐˜")`
Humidity is the amount of water vapour present in air. The air around us cannot hold more than a definite amount of water vapour at a given temperature. If the amount of water in air is already high, the rate of evaporation decreases. Therefore evaporation decreases with increase in humidity in surroundings.

`color{red}("๐Ÿ’ ๐–๐ˆ๐๐ƒ ๐’๐๐„๐„๐ƒ")`

With the increase in wind speed, the particles of water vapour move away with the wind, decreasing the amount of water vapour in the surrounding. Therefore evaporation increases with wind speed.

`color{green}("๐‚๐Ž๐Ž๐‹๐ˆ๐๐† ๐„๐…๐…๐„๐‚๐“๐’ ๐Ž๐… ๐„๐•๐€๐๐Ž๐‘๐€๐“๐ˆ๐Ž๐:")`

`color{green}(โ€ข)` In an open vessel, the liquid keeps on evaporating. The particles of liquid absorb energy from the surrounding to regain the energy lost during evaporation. This absorption of energy from the surroundings make the surroundings cold.

`color{green}(โ€ข)` When we pour some acetone over our palm then the particles gain energy from our palm or surroundings and evaporate causing the palm to feel cool.

`color{green}(โ€ข)` After a hot sunny day, people sprinkle water on the roof or open ground because the large latent heat of vaporisation of water helps to cool the hot surface.

`color{green}(โ€ข)` During evaporation, the particles at the surface of the liquid gain energy from the surroundings or body surface and change into vapour. The heat energy equal to the latent heat of vaporisation is absorbed from the body leaving the body cool. Cotton, being a good absorber of water helps in absorbing the sweat and exposing it to the atmosphere for easy evaporation.

`color{green}(โ€ข)` Let us take some ice-cold water in a tumbler droplets of water are seen on the outer surface of the tumbler. This is because the water vapour present in air, on coming in contact with the cold glass of water, loses energy and gets converted to liquid state, which can be seen as water droplets.