Explain the following temperature versus time graph:

The given graph represents the phase transitions of water with temperature. The plateaus on the curve show the phase changes. The temperature remains constant during these phase transitions. Line AB represents the conversion of ice into the water at a constant temperature. When ice is heated, it melts at 0 ° C and converts into water maintaining a constant temperature of 0 ° C . This constant temperature, at which the ice converts into water is called the melting point of ice. Also, during this transition, the ice absorbs heat energy from the surrounding water that is utilised for weakening the bonds between the atoms or molecules in the ice to transform itself into liquid water. This heat energy is called the latent heat of fusion. Once all the ice is transformed into water, the temperature of the water starts rising. It increases upto 100 ° C . Line BC in the graph represents a rise in the temperature of water from 0 ° C to 100 ° C . Thereafter, even though heat energy is supplied to water, its temperature does not rise. The heat energy is absorbed by water at this temperature is used to break the bonds between molecules of the liquid to convert the liquid water into a gaseous state. Thus, during the transformation from the liquid phase to the gas phase, heat energy is absorbed by the liquid, but its temperature remains constant. Line CD represents the conversion of liquid water into gas at a constant temperature. The constant temperature at which the liquid transforms into gaseous state is called the boiling point of the liquid. The heat energy absorbed at a constant temperature during the transformation of liquid into a gas is called the latent heat of vaporisation.