States of Matter

What are states of matter?

Most of the matter is present around us in three states- Solid, Liquid, and Gas. The states are the result of various differences in the particles of matter. These states, under certain circumstances like change in pressure, temperature, etc, are interconvertible from one form to another.


Solids are those matters which are densely packed. The space between two molecules of a solid is very less and their force of attraction is high. Due to these properties, solids are hard to bend(definite shape), are rigid(definite boundaries), and  can not be compressed easily(fixed volume).

On application of outside force, solids maintain their shape or may break.

Are rubber bands solid?

Rubber bands, being elastic in nature, have a tendency to expand when force is applied on them. However, as soon as the force is released, they regain their shape. So, we can say that rubber bands are solid.


Liquids on the other hand are loosely packed and hence are fluid in nature. Due to this, liquids don’t have a fixed shape, however they have fixed volume. They easily retain the shape of the container they are put in.

Gases like oxygen and carbon dioxide can dissolve in water. This property of liquids helps aquatic animals survive by providing them with essential gases for breathing.

We also know that solids such as salt and sugar easily dissolve in water.

Hence, we can say that all three states of matter can be diffused in liquids. This is because of free movements of particles in liquids.


Gases have the loose molecules with high kinetic energy. They move randomly at high speeds. The force of attraction between the molecules of the gases is very low and they are scattered making the gaseous state highly compressible. Liquified petroleum gas or compressed natural gas display of compressible property of gases.

Gases diffuse very fast in other gases. We can notice this when food is cooked. The smell of the delicious food reaches us even from far away. This is because the aroma particles from food diffuse with gases and travel fast to us.

All the states of matter, solid, liquid, and gas, occupy space. We can observe that a balloon, when filled with Helium gas, expands and hence we can say that the gas also occupies space. Due to random motion, particles of gases collide into each other or on the walls on the balloon exerting pressure per unit area.

Changing of the states of matter:

States of matter are inter-convertible. Sometimes they can also exist simultaneously in the environment like water. We find water in our environment in all three states, solid (as ice), liquid (as water), and gas (water vapour).

Changes affecting the States of matter: 

Change of temperature

Change in temperature in solids results in change in kinetic energy of the particles of energy. If we increase the temperature enough, the heat overcomes the forces of attraction between the particles and the particles begin to move freely. After some time at a point at a particular atmospheric pressure, also known as melting point, the solid is melted into it’s liquid form.

Melting point for ice is 273.15K. ( 0 degree = 273.15 kelvin). After reaching this point, the temperature of the system is not affected until the whole ice is melted. This hidden heat is known as latent heat.

Definition:The amount of heat energy required to change 1kg of a solid into liquid into liquid at atmospheric pressure at its melting point is known as latent heat of fusion.

Solids can also be converted into solid form directly. This process is called sublimation. We can observe this when we heat ammonium chloride.

Applying heat to water works in similar way. After acquiring enough energy to break free, the liquid starts changing into gas. This temperature at which a liquid starts boiling at the atmospheric pressure is called boiling point. Water boils at 373K.

The temperature after reaching boiling point stops increasing due to latent heat of vaporisation.

Cooling of gases can also convert them into solid or liquid states.

Hence, we can say that change in temperature can be a medium for change in states of matter.

Change of pressure

When pressure is applied, the distances between the particles of a matter reduce. Due to this, their states can be changed too. When we apply pressure and reduce the temperature, we can liquify or solidify the gases.

Carbon dioxide is often stored as dry ice in its solid state. It converts directly from solid to gaseous on decrease of pressure to 1 atmospheric pressure. This process of direct conversion of solid to gas is also called deposition.


Evaporation is the process by which water changes into its vapour form. We can observe it in everyday lives in activities like drying clothes, cooking, cooling of water in earthen pots, coolers and the water cycle.

Some factors affecting the rate of evaporation are:

Surface area:The increase in surface area of a surface increases the rate of evaporation.

Wind: It is easier to take away water droplets if wind is high.

Temperature: Increase in temperature increases the rate of evaporation.

From the above observations, we infer that states of matter are affected by temperature and pressure. When these factors change, we can also see a change in the state. We can also use this property of states of matter for our advantage like converting gases like petroleum gas into liquid form for use in cooking.

NCERT Solutions Related to the Topic States of Matter – NCERT Textbook Page 12

Question 3: Give reasons for the following observations.

  • Naphthaline balls disappear with time without leaving any solid.

Answer. Naphthaline balls go through the process of sublimation, they are converted directly from solid to gaseous state. Hence, they don’t leave any residue solid.

Question 4. Arrange the following substances in increasing order of forces of attraction between the particles- water, sugar, oxygen.

Answer. The order of increasing forces of attraction are: oxygen < water < sugar.

We can say this because gases have least force of attraction and are constantly in motion. Liquid particles though having greater forces of attraction are still fluid in nature. Solids posses very large force of attraction between the particles and are densely packed.

Question 5. What is the physical state of water at-

(a) 25 degree C : Water is liquid at room temperature.
(b) 0 degree C: Water is in solid state in the from of ice. It is the melting point of water.
(c) 100 degree C: On the boiling point of water, water starts converting into steam. Hence, water is in gaseous form.

Question 6: Give two reasons to justify-

(a) Water at room temperature is liquid.
Answer. Water at room temperature is liquid because its molecules don’t posses enough energy to overcome their forces of attraction and convert into gaseous form. They also have higher kinetic energy than that is required to make bonds strong enough to convert it into solid.

(b) An iron almirah is a solid at room temperature.
Answer. At room temperature, the particles in solids have very low kinetic energy and high forces of attraction. Because of this, they are in solid state, being rigid and hard.

Share on whatsapp
Share on facebook
Share on twitter
Share on linkedin
Share on email

Leave a Comment