3.2a During a physical change a substance keeps its chemical composition and proper-
ties. Examples of physical changes include freezing, melting, condensation, boiling,
evaporation, tearing, and crushing.
3.2b Mixtures are physical combinations of materials and can be separated by physical
3.2c During a chemical change, substances react in characteristic ways to form new
substances with different physical and chemical properties. Examples of chemical
changes include burning of wood, cooking of an egg, rusting of iron, and souring of
3.2d Substances are often placed in categories if they react in similar ways. Examples
include metals, nonmetals, and noble gases.
3.2e The Law of Conservation of Mass states that during an ordinary chemical reaction
matter cannot be created or destroyed. In chemical reactions, the total mass of the
reactants equals the total mass of the products.