Question

Define melting point of solid. Explain what happens when we supply heat energy to ice at $0{}^\circ C$ . Name the term used for the heat absorbed in the above process and define it.

Answer 1

Hint: Basically, melting point is the temperature at which solid changes to liquid state. The melting point of a solid and the freezing point of a liquid are the same.

Complete Solution :
Let us learn about the melting point firstly and then move forward for the illustration;
Melting point-
Melting, the word says that there is change in state from solid to liquid when heat is applied. The process of melting occurring at a specific and fixed temperature is called the melting point.
At the temperature, where the liquid and solid will be at equilibrium is known as melting point of solid or freezing point of liquid. Generally, for water this equilibrium occurs at $0{}^\circ C$.
\[{{H}_{2}}{{O}_{\left( s \right)}}\rightleftarrows {{H}_{2}}{{O}_{\left( l \right)}}\]

Now, When we supply the heat energy to ice at $0{}^\circ C$, melting will occur. The melting of a substance requires addition or supply of a characteristic amount of heat known as heat of fusion. Melting is also known as fusion as when the substances melt, the fusion takes place in the liquid state.
During melting, the heat absorbed by the ice is called latent heat. The change in temperature does not take place when ice absorbs latent heat. Thus, to melt the ice, we require external energy in the form of latent heat.

Latent heat-
The energy released or absorbed by a body or a thermodynamic system for a phase change, during a constant temperature process is known as latent heat. It can be stated as,
\[L=\dfrac{Q}{m}\]
where,
L = specific latent heat of any substance
Q = energy released or absorbed during the phase change
m = mass of the substance
The latent heat associated with melting of a substance is known as latent heat of fusion. It is usually stated as,
\[{{L}_{f}}=\dfrac{Q}{m}\]
where, ${{L}_{f}}$ = latent heat of fusion.

Note: Melting point is also sometimes known as liquefaction point. It is also similar to the freezing point or crystallisation point (rarely) of the liquid at equilibrium.