Changes in

Matter

Matter’s Changes and Properties• Physical Change

– properties remain the same

– changes the form of a substance without changing its identity

– All changes in state! (freeze, melt, condense, evaporate, and sublimate)

– Examples:• Boil, dissolve, break, split, crack, grind, cut, crush, and

bend.

Matter’s Changes and Properties

• Chemical Change– changes the identity of a substance

– a new substance is produced

– Examples: • rust, rot, burn, decompose, corrode, oxidize, ferment,

and explode!

– Evidence of a chemical change:• change in color or odor, formation of a gas, formation

of a precipitate (solid), change in light or heat

Matter’s Changes and Properties

• A physical change during digestion is the mechanical breaking up of food by teeth.

• A chemical change during digestion is the chemical breaking down of food in the mouth, stomach and small intestine with the aide of enzymes.

Matter and Change

Property

Solid Liquid Gas

Shape Volume

DefiniteDefinite

IndefiniteDefinite

IndefiniteIndefinite

Attractive Forces Strong Weak None

Expansion Very slight Moderate Great

Compressibility Almost none Almost none Readily

Atom Movement Vibration Flowing Free

Physical and Chemical Changes

• In a chemical reaction one or more substances change into new substances.

• The starting substances are called reactants and the substances formed are called products.

iron + sulfur iron sulfideor

Reactants Products

Law of Conservation of Mass• The Law of Conservation of Mass states

that the mass of all substances present before a chemical change is equal to the mass of all substances after the change.

10 g 10 g

Before Reaction After Reaction

Sometimes the mass of the reactants and the mass of the products appears to be unequal. This is usually because some of the mass is lost as a gas.

Wood + Fuel ash + released gas

99g + 1 g = 99.5g + 0.5g

Total Mass = 100g Total Mass = 100g

Law of Conservation of Mass

Although it appears mass is lost, 0.5g of mass is released into the air. The sum on both sides of the reaction is equal.