The phases of matter define the boundaries between the different states of matter and are associated with the organization and physical composition of matter. They define the different forms in which matter exists. Let us take a look at the different phases of matter and try to understand the processes of phase transitions.
Solid: When in solid state, the molecules of a substance are tightly bound to each other. As the molecules have a fixed position in space, a solid exhibits rigidity and possesses a distinct shape. The intermolecular distances in a solid are the least while the intermolecular forces of attraction are the strongest. When a substance in solid state is supplied with an amount of heat that raises its temperature to its melting point, the substance acquires a liquid state. There is an exception to this rule in case the solid substance is a sublimate. A solid that directly acquires a gaseous state on heating is known as a sublimate. Camphor is an example of sublimates. Examples of solids include, wood, iron, ice, rock, etc.
Liquid: The forces of attraction between the molecules of a liquid are less than those in a solid and greater than those in a gas. A substance in liquid state does not have a defined shape; rather, its shape is defined by that of its container. When a liquid reaches its boiling point, it acquires a gaseous state. If heat is removed from a liquid by cooling it, it changes to a solid state on reaching its freezing point. Examples of liquids include, water, blood, mercury, milk, etc.
Gas: Gas molecules are in a state of random motion. They exhibit the least intermolecular forces of attraction and hence gases lack a definite shape. The intermolecular distances are very large due to which the particles of gases are widely separated from each other. The density and viscosity of a gas is less as compared to solids and liquids. Gas molecules are highly vulnerable to the changes in temperature and pressure. When a gas is cooled, it acquires a liquid state, which on further cooling obtains a solid state. Examples of gases include air, water vapor, helium, ozone, etc.
We are generally taught about the three states of matter mentioned above. It is relatively less known that matter in fact exists in more than just three distinct states. Here are the other four.
Plasma: A gas that is composed of freely floating ions is known as plasma. The free-floating ions are atoms, which obtain a positive charge on account of losing some of their electrons. The ions can also be in the form of free electrons. Thus, the positive and negative charges can move independently, making plasma molecules electrically conductive. Plasma does not have a defined shape and takes the form of gas-like clouds. As the properties of plasma are totally different from those of solids, liquids and gases, plasma is considered as a separate state of matter. Examples of plasma include auroras, welding arcs, and lightning.
Bose-Einstein Condensate: A substance in this state of matter consists of bosons cooled to temperatures nearing absolute zero. Most of the atoms collapse into the lowest quantum state of external potential. Under these conditions, the quantum effects are seen on a larger scale.
Supercritical Fluid: The temperature and pressure conditions under which the boundary between phases of matter does not exist, is referred to as the critical point of a substance. When a substance is at a temperature and pressure above its critical point, it is known to be in the supercritical fluid state. In this state, a substance shares the property of diffusion with gases and adopts the property of liquids of dissolving materials.
Degenerate Matter: In this phase, matter has a very high density. The pressure that the degenerate matter maintains is known as degeneracy pressure. It is predominant at high densities. Increase in the temperature of degenerate matter has little effect on its total pressure. At very high temperatures, thermal pressure increases. One of the well-known examples of degenerate matter is the strange matter, which is believed to occur in neutron stars.
What's interesting about the different phases of matter is that there is a wide variety in the forms in which a substance can exist. Think of it and you will understand how the same substance can exist in four or five different forms, exhibiting different physical properties. It is interesting to see how temperature and pressure conditions cause transitions in the different phases of the matter that makes up our universe.