CHANGES

PHYSICAL PROPERTIES Physical property- characteristics of a material that can be observed without changing the identity of the substances in the material. These include color, shape, size, density, melting point, and boiling point

Appearance- Physical description of a substance Appearance- Physical description of a substance. (color, shape, size, density) Behavior- How a substance acts. (magnetism, viscosity, ductility) Observations- Start and end with the same substance

PHYSICAL CHANGE Physical change- Change in a substance’s size, shape, or state of matter. Substances do not change identity when it undergoes a physical change.

PHYSICAL CHANGES EXAMPLES Biting Melting cutting

More Examples breaking a glass haircut adding chocolate squeezing syrup to ice cream squeezing a wet sponge

CHEMICAL PROPERTIES Chemical property- characteristic of a substance indicating that it can change chemically. (flammability, light sensitivity)

Chemical Change Chemical Change- When one substance changes to another substance a chemical change has occurred. Some indicated by temperature change, color change, noticeable smell, gas production or formation of a precipitate Others occur slowly. – rust

CHEMICAL CHANGES EXAMPLES SALIVA, STOMACH ACID, ENZYMES (chemicals which speed up reactions) Rust/Tarnishing FIRE-burning

EVIDENCE OF CHEMICAL CHANGES

WEATHERING Weathering- involves both chemical and physical changes. Physical- ex: big rocks split into smaller ones, streams carry rocks from one place to another Chemical- ex: occur in rocks when calcium carbonate in limestone changes to calcium hydrogen carbonate due to acid rain

Energy in Reactions

Bonding and Energy Energy is required to break chemical bonds. Energy is released when chemical bonds are formed.

Chemical reactions can also be categorized into two types Endothermic Reactions Exothermic Reactions

Endothermic Reactions

Sucks in the heat Turns cold Absorbs energy - heat

Endothermic (in-heat) Reactions absorb heat by absorbing energy Sometimes called endergonic

Endothermic Temperature of the products may be less than temperature of reactants This type of reaction produces a decrease in temperature

Endothermic Examples : Baking soda and vinegar Instant cold packs

Exothermic Reactions

Releases energy - heat

Exothermic (out-heat) Reactions that produce heat by releasing energy Sometimes called exergonic

Exothermic Temperature of products is usually greater than temperature of reactants This type of reaction produces an increase in temperature

Exothermic Examples : Hot hands Bunsen Burner-lit Candle Combustion in car engine

Why isn’t freezing water an endothermic reaction?