The Phases of Matter

In our everyday life, we encounter matter in three different states, or phases (the word comes from the Greek for “appearance” or “manifestation”). These states are the solid phase, the liquid phase, and the gas phase. The temperatures at which a material melts—changes from solid to liquid—and boils—changes from liquid to gas—are determined by the bonding forces among the atoms or molecules. The stronger the bonds, the more energy needed to overcome them, and so the higher the temperature at which the material shifts from one phase to another. During that shift, all the heat added to the material goes into completing the phase change. The temperature of a solid-liquid mix will remain fairly constant until all the solid has melted. Similarly, the temperature of a pot of boiling water on a high flame remains constant—at the boiling point—until all the liquid water has been turned into steam.