Question

Why does the temperature of a substance remain constant during its melting point or boiling point?

Answer 1

Melting and boiling points

• The melting point of a solid is the temperature at which it melts to become a liquid at atmospheric pressure.
• At atmospheric pressure, the boiling point of a liquid is the temperature at which it boils and transforms rapidly into a gas.

Reason for not an increase in temperature

• When a solid, such as ice, is heated, it begins to melt. However, even after a constant source of heat, the temperature does not rise until all of the ice has melted.
• The excess heat is used to melt all the particles of ice through a process known as latent heat of fusion.
• Similarly, when a liquid, such as water, begins to boil, the temperature of the liquid does not rise as a result of the constant input of heat.
• The excess heat given to boiling water is used to vaporize water, which is known as latent heat of vaporization.
• So, the temperature does not rise because the heat supplied is constantly consumed by overcoming the forces of attraction between the particles in order to change the state of the substance.