Question

Define the following terms
    (A) Melting point
    (B) Boiling point
    (C) Evaporation

Answer 1

Hint: The given terminologies are related to phase transitions. Phase transition is when a substance changes its state from solid, liquid or gas to a different state. A phase transition occurs as a result of the change in external conditions such as pressure, temperature etc.


Complete step by step solution:
 - A substance can have three states to change into. They are solid, liquid and gas. As we know every substance is in one of these three phases at certain temperatures. The conditions of temperature and pressure at which the substance will change its phase depend on the intermolecular forces of atoms and molecules.
- The Melting point is the temperature at which a material in solid phase is converted to liquid at normal atmospheric pressure. Each substance has a different melting point. Different temperatures are required to melt a substance at different pressures. At the melting point, the solid and liquid phase exists at equilibrium.
 - Melting point of a compound is determined by the intermolecular attraction and symmetry. If the intermolecular forces are stronger, higher would be the melting point. We all know that ionic compounds usually have higher melting points. It happens because the ion-ion interaction of electrostatic forces is highly strong.
 - At the boiling point a liquid is converted to a vapour. Hence boiling point can be defined as the temperature at which the atmospheric pressure of the liquid's environment becomes equal to vapour pressure of the liquid. Thus, boiling point of a liquid depends upon the liquid's temperature, atmospheric pressure and vapour pressure.
 -As in the case of melting point, each substance carries its own boiling point. For example, the boiling point of water is 100${}^\circ C$ at 1 atm.
- Evaporation can be defined as the process in which a substance in liquid state changes into the gaseous state due to a change in temperature or pressure. If we take water as an example, then by evaporation liquid water gets transformed into water vapour
- If we look deep into the concept of evaporation, we can understand that there are certain conditions to be satisfied and they are molecules located near the surface, moving in proper directions and molecules should have sufficient kinetic energy to overcome liquid-phase intermolecular forces. Also is dependent on temperature. It proceeds quickly at higher temperatures.


Note: Evaporation and boiling are generally confused with each other. It has to be noted that evaporation is the process where liquid gets converted to vapour and boiling refers to the process of heating up a liquid where the temperature of liquid that is being heated up is greater than the boiling point of substance.