Chemical/Physical Changes and Properties

Physical Properties can be measured or observed without changing the identity (or composition) of a substance.

– The chemical make-up is not changing

when these properties are observed!

– Examples : color, odor, texture, taste, freezing point, melting point, density, mass, hardness...

Chemical Properties

• Properties that indicate how a substance reacts with other substances

– These properties are only observed when the substance undergoes a chemical change

– Examples: flammable, combustible, burnable, change in color, “reacts with...”

Law of Conservation of Mass - In any chemical or physical change, matter cannot be created or destroyed.

Chemistry: The study of matter and the changes it undergoes.

Matter: anything that has mass and volume (EVERYTHING!)

Mass: the amount of matter in an object (How much “stuff”)

Energy: Anything that can do work or produce heat.

Weight: The force of gravity acting on an object’s mass.

Pure Substances

• Have uniform and definite composition

–Elements: found on the Periodic Table (approx. 118)

•Described by symbols: H, He, etc.

–Compounds: formed when elements chemically combine: H2O, CO2, NO2

Mixtures

• Two or more pure substances physically mixed together.

–In compounds, the elements are bonded to each other

–In mixtures, the substances are blended

–No definite composition – cannot assign a fixed ratio (ex: H2O)

Two Types of Mixtures:

• Heterogeneous mixtures: does not

have a uniform composition

– Parts of the mixture can be physically

seen and “picked out” of the mixture

– Examples: Cereal, pizza, salad

– (2) Categories

• Colloids

– Emulsions - sub-class of colloids

• Suspensions

Homogeneous mixtures: has a

uniform composition

–Parts of the mixture cannot be

“picked out”

–Examples: sugar water, milk

–(1) Category

• Solutions (solvent + solute)

– metal alloys - a type of solution

Solute + Solvent = Solution

SOLUTE dissolves in the solvent

SOLVENT does the dissolving of the solute ex) Sugar water sugar is the solute; water is the solvent

endothermic- the reaction loses heat

exothermic-reaction gains heat

A solid has a definite shape and definite volume with a high density and is not compressible

A liquid has an indefinite shape and definite volume with a density less than solids and is not compressible

A gas has an indefinite shape and indefinite volume with a low density and is compressible