Observing Chemical ChangeObserving Chemical Change

How can changes in matter be described?How can you tell when a chemical reaction

has occurred?

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Only three NEW vocabulary words!

Vocabulary ReviewVocabulary Review 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 ChangeBonding and Chemical ChangeChemical changes occur when bonds break and new bonds form.

Evidence for Chemical Evidence for Chemical ReactionsReactions 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 ReactionsMore 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 ReactionReview Endothermic ReactionChemical 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: Review: ExothermicExothermic Reaction Reaction

The making or breaking of chemical bonds results in a net release of energy

Energy typically releases as heatFuel 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 ChangeBonding and Chemical Change