Evidence of Chemical Evidence of Chemical ReactionsReactions

Unit 5Unit 5

How do you know a chemical How do you know a chemical reaction has occurred?reaction has occurred?

Unlike a physical change, where no Unlike a physical change, where no substances are created, a chemical substances are created, a chemical change creates new substances by change creates new substances by rearranging atoms.rearranging atoms.

Law of Conservation of Mass –states Law of Conservation of Mass –states that during a chemical reaction, that during a chemical reaction, mass is neither created nor mass is neither created nor destroyed. destroyed.

Evidence of a Chemical Evidence of a Chemical ReactionReaction

Precipitation – a Precipitation – a solid is created.solid is created.

Evidence of a Chemical Evidence of a Chemical ReactionReaction

A gas evolvesA gas evolves

Evidence of a Chemical Evidence of a Chemical ReactionReaction

Formation of Formation of water- water-

Evidence of a Chemical Evidence of a Chemical ReactionReaction

Changes in energy Changes in energy to the systemto the system It gets colderIt gets colder It gets hotterIt gets hotter