Can matter change its state? Have you ever given a thought to what the various things around us are made up of? Everything in this universe is made up of material which the scientists refer to as �Matter�. The matter exists in three states namely- Solid, Liquid, and Gas. Let us understand how the interconversion of states of matter takes place.

 

An interesting example to understand the states of matter is water since it can exist in all the 3 states. Ice is the solid state of water that exists at and below a temperature of zero degrees celsius. Water is liquid, and Vapors or steam is the gaseous state of water.

 

The liquid state, that is, water can be converted into ice by freezing, and similarly, the gaseous state, that is, water vapor can be achieved by boiling the water. In a similar manner, ice can be converted into water by raising the temperature. We can thus infer that one state of matter can be converted into another state by:

� Changing the temperature
� Changing the pressure.

 

Effect of temperature on states of matter

 

We know that matter around us exists in three different states namely solid, liquid and gas, and also that matter can change its state. But how does this change in the state of matter occurs? The temperature has an important role here. Let us find out how.

 

On increasing the temperature of solids, the kinetic energy of the particles increases which sets them into motion. The heat supplied overcomes the forces of attraction between the particles and the particles, therefore, start moving more freely. And, the solid eventually melts into a liquid.

 

The amount of heat energy that is required to change one kilogram of a solid into liquid at atmospheric pressure is known as latent heat of fusion, and the temperature at which it occurs is known as its melting point. The process of melting is also termed fusion.

The melting point of a solid depends upon the strength of forces of attraction between the particles. The higher the strength of forces of attraction, the higher is the melting point.

 

Let us learn some more facts regarding the fusion of solids. On heating some ice in a beaker at a low flame, you will observe that ice melts at a temperature of zero degrees Celsius or 273.16 Kelvin.

 

It is also observed that even when the melting starts, the temperature of the system remains constant till the entire solid melts, even though heat is being continuously supplied. You must be wondering where this energy goes? Isn�t it?

This heat energy is actually used up in overcoming the forces of attraction between the particles of the solid during the change of state from solid to liquid. As there is no increase in kinetic energy of the particles, the temperature of the system also does not show any rise during the change of state. The heat, therefore, gets hidden within the contents of the beaker and is called latent heat.

 

Do you know that the particles in water have more energy as compared to particles in ice at a temperature of 0 degrees celsius? Let us find out why.

Heat energy (equal to the latent heat of fusion) absorbed during the change in state is used up in overpowering the strong attractive forces between the particles. The temperature of the system, therefore, does not change even when the melting point is attained till all the ice melts into water. However, the absorbed heat gets hidden in the contents of the container.

 

On the other hand, lowering the temperature causes the reverse process. The kinetic energy of the particles decreases and the attractive forces pull the particles close together. On further lowering the temperature, the substance eventually freezes, that is, the liquid changes into a solid.

 

This change of state from liquid to solid is called freezing and the temperature at which the liquid freezes is called its freezing point. It is interesting to note that the freezing point of a liquid is the same as the melting point of its solid state.

 

Change of liquid to a gaseous state

 

We are already aware that increasing temperature can convert a solid to liquid. Let us now learn what happens to the liquid, so formed, when the temperature is increased further. When heat is further supplied to the liquid, the kinetic energy of the particles further increases which results in an increase in the inter-particle distance, and the force of attraction between the particles weakens.

Eventually, a stage is reached when the particles possess enough energy to break free from the forces of attraction holding them together and to move about freely in space. At this temperature, the liquid starts changing into vapors, that is, to the gaseous state.

 

The temperature at which the liquid starts boiling at the atmospheric pressure is called its boiling point. You must be aware that water boils at a temperature of 100 degrees Celsius, that is, 373 Kelvin. It is observed that during the change of state from liquid to gas, the temperature of the system remains constant till the entire amount of liquid is converted into vapors, even on continuously supplying heat.

This is because the heat supplied is actually used up in overcoming the forces of attraction between the particles of the liquid without increasing their kinetic energy. Since the absorption of heat is not accompanied by an increase in temperature, the heat thus absorbed is called the latent heat of vaporization.

 

The latent heat of vaporization can also be defined as the amount of heat energy required to convert one kilogram of a liquid into vapors at atmospheric pressure at its boiling point. It is also due to a higher latent heat of vaporization, that though they exist together at 100 degrees Celsius, particles of steam have more energy than those of water. It is for this reason that burns caused by steam are much more severe than those caused by boiling water.

 

Change of solid to a gaseous state

 

Instances of solids converting to liquids and liquids converting to gases when heated are aplenty. It is interesting to note that a solid may be converted not only to the liquid state but also to the gaseous state.

 

There are some substances which upon heating change directly from solid to a gaseous state and vice-versa upon cooling. There is no intervening liquid state. This process is called sublimation.

 

Ammonium chloride, Camphor, Naphthalene, Anthracene, Benzoic acid, Iodine, etc. are some examples of such substances that commonly undergo sublimation on heating.

 

Change of gaseous to liquid state

 

We are already aware of the effect of increasing the temperature on the interconversion of states of matter. But do you know what happens when a gas is cooled? When a gas (or vapors) is cooled by lowering the temperature, the kinetic energy of its constituent particles decreases due to which the particles start moving slowly.

On further lowering the temperature, the attractive forces pull the particles close together and the gas (or vapors) condenses to liquid. This process of change in the state of a gas (or vapors) to a liquid by cooling is called condensation.

 

Effect of pressure on states of matter

 

We already know that difference in the three states of matter is mainly due to the difference in the inter-particle distance which arises because of:

 

• The difference in the size of constituent particles, and also
• The magnitude of the forces of attraction between these particles.

 

We have also noted that inter-particle distances are the largest and inter-particle forces of attraction are the weakest in the case of gases. On the other hand, the inter-particle distances are shorter and the forces of attraction stronger in liquids, while they are the shortest and the strongest respectively in the case of solids.

 

It is interesting to note that a gas can be converted into liquid if the inter-particle distance is reduced.
And the inter-particle distances can be reduced either by:

 

• Applying pressure
• Lowering temperature
• By combining both these factors

 

We have already learned the effect of temperature on the states of the matter earlier. Let us now see what effect the change in pressure brings about on the states of matter. If we apply pressure to gas by compressing it with a piston in a cylinder, the gas compresses to a small volume.

This decreases the inter-particle distance by bringing the particles closer. The particles thus start attracting one another more strongly and form a liquid. We can therefore infer that the application of pressure can liquefy a gas.

 

Have you ever heard about dry ice? Let us find out what it actually is.

 

If carbon dioxide gas is cooled under high pressure, it directly converts into solid carbon dioxide which is famously known as the �dry ice�. This dry ice is stored under high pressure because the pressure on dry ice falls to one atmosphere, it sublimes directly into the gaseous state.

Read More: States of Matter: Solid, Liquid and Gas | Effect of Temperature