Observing Chemical Change How can changes in matter be described? How can you tell when a chemical reaction has occurred? √ Only three NEW vocabulary words! √ √ √ √ √ √ √

Vocabulary Review Reactants and products Matter-anything that has mass and takes up space Chemistry-the study of matter and how matter changes Physical properties and Chemical properties Physical and Chemical change (salt in water versus burning wood) Reactants and products

Bonding and Chemical Change Chemical changes occur when bonds break and new bonds form.

Evidence for Chemical Reactions Change in properties and change in energy (only sure evidence) Change in physical properties…new substances color Precipitate (solid formed during a chemical reaction) A gas from solid or liquid reactants Physical properties such as texture and harness may also change Moist dough becomes a dry, porous solid after baking

More on Chemical Reactions Changes in chemical properties Na and Cl are reactive elements but their product (NaCl) is stable One or more new substances are produced in a chemical reaction When an electric current is passed through water (electrolysis) H2 (gas) and O2 (gas) are produced.

Review Endothermic Reaction Chemical reactions occur when bonds break and new bonds form. They usually absorb heat or liberate heat(release it). Endothermic reactions absorb energy when the bonds break Energy is absorbed from nearby matter Often temperature changes Baking soda combined with vinegar absorbs heat, making it feel colder When heat is added constantly, (egg frying)

Review: Exothermic Reaction The making or breaking of chemical bonds results in a net release of energy Energy typically releases as heat Fuel and oxygen in the plane’s engine release heat causing the gases in the engine to expand. This moves the gases out of the plane which exerts a force that moves the plane forward.

Bonding and Chemical Change