Melting

Melting

A substance absorbs heat energy and it melts. The temperature at which a substance melts is called as melting point. Different substances have different melting points. Hard substance such as diamond also melts.

Melting points of a few substances

1. What happens when a solid is heated until it melts?

How temperature of a solid does varies on heating?

Melting point apparatus set up is as shown below. We can study the melting of solid naphthalene by varying the temperature with time.

Let us observe the variation of temperature of the solid while it is heated at regular intervals of time. We can continue heating till entire solid melts and a little beyond. If we plot a graph of temperature versus time, we get a melting curve as shown below.

Melting Curve

From the graph what conclusions can we get?

Let us try to answer the following questions.

Let us now analyse the curve.

Why the temperature remains constant between B – C?

The entire heat energy absorbed is used to overcome the attractive forces between the solid particles, which are held in xed positions. Hence, there is no increase in temperature. is hidden energy is called latent heat of fusion, which is exclusively used for change of state from solid to liquid.