Chemistry students recently explored changes in matter, which are classified as either physical or chemical. Although some changes are straightforward, others are so closely related that it can be difficult to determine the difference. When the matter is altered, but the chemical composition remains the same, it is a physical change. With a chemical reaction, the atoms of a substance are rearranged. Common indicators that may suggest a new substance are changes in color, development of odor, evolution of gases, and formation of precipitates. Students measured the mass of the materials before and after the changes and recorded their data, observations, and conclusions.