To summarize our discussion assume that ice at a temperature less than 0°C is being heated. Its temperature continuously increases until it starts to melt at 0°C (melting point of ice). This temperature remains constant until all of the ice melts to water. Once all of the ice becomes water at 0°C the temperature again starts to increase until it starts to boil at 100°C (boiling point of water). This temperature in turn remains constant until all of the water vaporizes to gas (vapor). If the gas continuous to be heated starting above 100°C its temperature increases as required. The diagram that shows all these processes is known as the heating curve, See Figure 16. It is also possible to draw the cooling curve using the same concept.