In this topic you will learn how matter can be changed in two basic ways: chemically and physically.

A chemical change produces new matter with properties different from those of the original matter. In a chemical change you start with one kind of matter and end up with another.

You can find evidence of chemical changes all around you. In a chemical change, the product has properties that are different from those of the original elements or materials. When the chemical change makes a new substance the product is a compound. Sometimes the product is the elements making up the compound (when the chemical change breaks compounds apart). Energy is always involved in a chemical change.

Some compounds that are formed by chemical changes are beneficial, while other compounds can be harmful. Some of the effects of harmful compounds can be prevented or slowed down.

Matter can also change through physical means. A physical change begins and ends with the same type of matter, but may involve a change in size or shape. The original properties of the matter do not change even if it is cut, folded, or stretched.

Change in position or texture is a second kind of physical change. The original properties of matter do not change even if it is moved, rearranged, or crumpled. Change of state is a third kind of physical change. The properties of matter do not change even if it is melted, frozen, or heated.

Some types of matter can exist in more than one state. Heat energy can change the state of matter. Heat energy makes the particles of matter move. The more heat energy matter has, the faster its particles move. Taking away heat energy slows particles down. Particles in a solid do not move very much. If enough heat energy is added, the solid may melt and form a liquid. Liquid particles form groups that slide past one another. Adding more heat energy causes the particles to move so fast that the liquid breaks up. Some particles may escape as a gas. Adding more heat breaks up groups of particles completely.

Understanding how to use our knowledge of chemical changes has allowed people to mix elements and materials to create many products. These products make our lives more enjoyable, healthy, and convenient.