The graph above called a heating curve, representing the changes that occur when 1.00 mole of water is heated from −25 ^oC to 125 ^oC at a constant pressure of 1 atm.

• Blue lines show the temperature increase within a phase.

• Red lines show the conversion of one phase to another at constant temperature.

All the added energy is used to overcome the attractive forces between the molecules rather than increase their kinetic energy.