boiling means matter / a substance changes from a liquid into a gas by increasing heat energy & water is a kind of substance & water is in a boiling process ->  the heat energy of water is increasing  the heat energy of water is increasing & temperature is a measure of heat energy ->  the temperature of water is increasing  the temperature of water is increasing & water is a kind of substance & as the temperature of a substance increases , the molecules in that substance will move faster and farther apart -> the water molecules will move faster and farther apart