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Explore physical and chemical properties, reactions, and examples like rust, fire, and weathering. Learn about endothermic and exothermic reactions and the energy involved in chemical bonding.
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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. (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 CHANGESEXAMPLES Biting Melting cutting
More Examples breaking a glass haircut adding chocolate 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
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
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