Ch 04.6: Chemical Changes

chemical change

- a change in matter in which the substances that make up the matter change into other substances with different chemical and physical properties

- the new substance produced has different chemical and physical properties than the original substance

- also called a chemical reaction

Many times, changes in physical properties are the only signs that a chemical change has occurred.

- the only sure sign of a chemical change is the formation of a new substance

formation of a gas

- bubbles, fizzing, or odor

formation of a precipitate

- a solid (new substance) that sometimes forms when two liquids combine

unexpected color change or rusting

the release of thermal energy (unexpected temperature change)

the release of light, loud sound, smoke, or fire

tarnishing

food spoiling

Chemical changes often cannot be undone. Some can be reversed, but only by other chemical changes.

The total mass of a substance does not change during a physical or chemical change.

Law of Conservation of Mass - the total mass before a chemical reaction is the same as the total mass after the chemical reaction