Question

How do phase changes occur on a molecular level?

Answer 1

Hint:To answer this question we should know what does a phase change means and what molecules are. Molecules are formed by the combination of atoms in a fixed ratio. Molecules are held together by some force of attraction to give compounds or substances. The different phases of the substance differ based on the forces present between the molecules. During the phase transition, the strength of the forces gets changed.

Complete answer:A substance can have three phases, solid, liquid, and gas. At a time a substance can exist in one phase only.At some fixed conditions of temperature and pressure, two phases can remain in equilibrium for some time, and as the conditions change the amount of substance in one phase increases, and the amount of substance in another phase decreases. This process is known as phase interconversion.In a solid-state, the molecules are compactly bound with each other by a strong force of attraction. In the liquid state, the molecules have fewer attraction forces.We will consider the conversion of solid water to liquid water to understand the change at the molecular level as follows:As we start heating the solid water means we melt the ice, the heating gives the energy to water molecules, so the intermolecular forces present between solid water molecules break, and molecules go apart. This increases the randomness of the water molecule and solid water converts into a liquid at the melting point of ice, the solid and liquid remain in equilibrium.

Therefore, the phase changes occur on a molecular level by altering the strength of intermolecular forces.

Note:The phase interconversion depends upon the temperature and pressure. The conversion of solid into liquid is known as melting and the reverse process is known as freezing. The conversion of liquid into a gas is known as vaporization. The conversion of solid into gas is known as sublimation. The forces present in between two molecules are known as intermolecular forces. The strength of intermolecular forces can be decrease or increase. It depends upon the phases which are interconverting.