How does a chemical change affect the composition of matter?
A physical change in matter is a change in one or more of matter's physical properties. In a physical change, matter may change its size, shape, or state, but its chemical properties do not change. Because the chemical properties of matter remain the same in a physical change, a physical change is often easy to reverse. A chemical change occurs whenever matter changes into an entirely different substance with different chemical properties. Burning is an example of a chemical change. Signs of chemical change include the release of bubbles, a change of color, production of an odor, release of heat and light, and production of loud sounds. Because chemical changes result in different substances, they often cannot be undone. Some chemical changes can be reversed, but only by other chemical changes.