1. Formation of a gas: When a substance undergoes a chemical change, it may produce a gas as a result of the reaction. For example, when magnesium metal (Mg) reacts with hydrochloric acid (HCl), it produces hydrogen gas (H2) in a chemical reaction that forms magnesium chloride (MgCl2).
2. Change in energy: Chemical changes often involve the exchange or generation of energy. An example of this is the reaction between baking soda (sodium bicarbonate, NaHCO3) and vinegar (acetic acid, CH3COOH), which produces carbon dioxide gas (CO2) and releases energy in the form of heat.
3. Formation of a precipitate: In some chemical reactions, when two substances react, a solid precipitate may form as a result of the reaction. An example of this is when silver nitrate (AgNO3) reacts with sodium chloride (NaCl) to produce silver chloride (AgCl), which is a solid precipitate.