GACE Elementary Education II Practice Test

The main idea is that a change which creates one or more new substances is a chemical change. In a chemical change, atoms break apart and recombine to form substances with new properties. That’s why you often see new odors, colors, bubbles, or a precipitate appear, and why the material may release or absorb energy as bonds are formed or broken. Physical changes, on the other hand, don’t produce new substances. They involve changes in size, shape, or state (like ice melting to water), but the chemical identity remains the same. A phase change is a specific type of physical change where a substance changes from solid to liquid or liquid to gas, again without changing its chemical composition. Reversible change describes whether the process can be undone, but it doesn’t by itself indicate whether a new substance is formed; some changes can be reversed and still involve no new substances, while some chemical changes can be reversible too. So, only a chemical change results in substances with new chemical identities.