Physical and chemical changes

• Physical Property: A characteristic of that can be measured without changing the chemical composition of a substance.

• Ex. Color, shape, size, density, melting point, boiling point, hardness, conductivity, malleability, ductility, state

                                                                                                                             

                                                                    Slide 8 of 10

• Physical change: a change which does not change the identity of the substance

• Ex. Boiling, melting, changing shape, mixing, freezing, dissolving

• Chemical change: A change where a new substance is formed from other substances, and has new properties

• Burning O2 and H2 gives off H2O and energy

• Chemical property: A characteristic of a substance which indicates whether it can undergo a specific chemical change

• Ex. Flammability, reactivity, or non-reactivity

Signs of a Chemical Change

• color change, • formation of a

precipitate, • gases given off, • energy change-

heating up or cooling down, light,

Signs of a reaction

• Precipitate: substance formed when a solid forms out of two liquids

Energy change

• Endothermic: chemical reaction that absorbs energy or heat

• Exothermic: chemical reaction gives off energy or heat

Exo vs. endo

Law of conservation of mass

• Law of Conservation of mass: mass of all substances before a chemical reaction is equal to the mass of all substances after the reaction

• •Extensive physical

• –Depend on the amount of the material present (ex. mass, length, & volume)

• •Intensive physical

• –Does not depend on the amount of material present (ex. density, boiling point, ductility, malleability, color)

Boiling Point

• Boiling point- Temperature at which vapor pressure overcomes atmospheric pressure.

• Does Water always boil at 100ºC

• Why or why not?

• What would it do in space?