States of Matter
There are five main states of matter. Solids, liquids, gases, plasmas, and Bose-Einstein condensates (BEC) are all different states of matter. Each of these states is also known as a phase. Elements and compounds can move from one phase to another when specific physical conditions are present. One example is temperature. When the temperature of a system goes up, the matter in the system becomes more excited and active. Scientists say that it moves to a higher energy state. Generally, as the temperature rises, matter moves to a more active state.
Think about it this way. Remember that glass of water (H2O) we talked about? When the temperature of the water goes up, the molecules get more excited and bounce a lot more. If you give a liquid water molecule enough energy, it escapes the liquid phase and becomes a gas. Have you ever noticed that you can smell a turkey dinner after it starts to heat up? As the energy of the molecules inside the turkey heat up, they escape as a gas. You are able to smell those volatile gas molecules.
A "phase" describes a physical state of matter. The key word to notice is physical. Things only move from one phase to another by physical means. If energy is added (like increasing the temperature) or if energy is taken away (like freezing something), you have created a physical change.
A compound or element can move from one phase to another, but still be the same substance. You can see water vapor, in the form of steam, over a boiling pot of water. That vapor (or gas) can condense and become a drop of water. If you put that drop in the freezer, it would become a solid piece of ice. No matter what phase it was in, it was always water. It always had the same chemical properties. On the other hand, a chemical change would change the way the water acted, eventually making it not water, but something completely different. If you added a carbon (C) atom to a water molecule, you would have formaldehyde (H2CO), and that is nothing like water.
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