One day Sohan came to home from school at lunch time.

He was suffering from fever. When he reached home, he did not find anyone at home.

He called his mother and came to know that she had gone to market. He searched for water in the house.

But he only found ice-cooled water in the refrigerator. He took the ice-cooled water and boiled it.

While he was heating the water, he observed the bubbles and quick transformation of ice into the boiling water.

He was little surprised by observing how the ice cubes were transforming into vapour and how the water level has decreased in the container.

He thought for a moment and discussed with his friends. Then, he came to know that the conversion of ice to steam can be explained by the heating curve.

So let's understand the heating curve.

The heating curve of any substance represents the variation of temperature with heat energy.

The heating curve of a substance consists of various intermediate stages to convert it from one phase to another phase.

Now, let's discuss the heating curve of ice.

The heating curve of ice also consists of some intermediate stages during the conversion of ice to vapor..

Let us suppose a container having a block of ice.

Suppose the mass of the ice block is $m$ gram while its temperature is -30 $°$C.

As we provide heat to this system, the ice block absorbs it and thus, its temperature increases.

The temperature of the block will increase till it reaches the melting point of ice.

Let us suppose that the $H_{1}$ heat is required to convert $m$ gram of ice from -30 $°$C to 0 $°$C.

This conversion can be represented on a graph where $y−axis$ represents the temperature and the $x−axis$ represents heat.

The heat provided and slope for the temperature-heat curve in the solid phase can be calculated as,

Since the slope is constant, the heating curve in this region will be a straight line from $a$ to $b$.

If we keep on providing heat to the ice block after reaching 0 $°$C then, the temperature will not change.

There will actually be a change of phase from $b$ to $c$ that requires the latent heat of fusion, let say, $H_{2}$.

The heat required for phase change and slope needed can be calculated by the formula,

This phase change can be plotted on the graph which is shown by $bc$ ,

At point $c$, the complete ice will be converted into the water and if we keep on providing heat, then the temperature will further increase in the liquid state.

Let us assume $H_{3}$ be the amount of heat required to raise the temperature of water from 0 $°$C to 100 $°$C.

We can find the heat $H_{3}$ from the heat formula as,

Now, we can plot the process $cd$ on the heating curve as,

If we further provide heat to the water after point $d$, then the temperature will not change but again a phase change will occur.

Let us assume $H_{4}$ amount of heat is required to convert water into vapour.

We can represent the phase change $de$ on the heating curve as,

If we will further provide heat to vapour, then it will only increase its temperature. There will be no phase change. The vapour in this form will be known as superheated vapour.

Let us assume $H_{5}$ amount of heat is required to heat the vapour to its superheated form,

The rise in the temperature in gaseous phase can be represented by the process $ef$ on the heating curve.

Finally, we can represent the complete heating of ice and its conversion into the gaseous phase on the heating curve.

Revision

The heating curve of any substance represents the variation of temperature with heat energy.

We can represent the heat required at various stages to convert ice into vapour by a block diagram.

The heating curve of conversion of ice to vapour can be represented as,