Chemistry

Mrs. Algier

Do Now: Complete matter classification worksheet.

YWBAT

• Differentiate between physical and chemical properties.

• Differentiate between physical and chemical changes.

Physical Property

• Characteristic that can be observed or measured WITHOUT changing the substance’s composition

• Examples– State (Solid, Liquid, Gas)– Color– Melting Point

Chemical Property

• Chemical Property - Properties that can only be observed when we attempt to change the identity of a material

• Example– The ability to rust is a chemical property of iron.

Iron combines with oxygen to form rust.

Physical or Chemical Property?

• Blue Color• Density• Flammability• Melting Point• Reacts with acid to form Hydrogen• Burns• Boiling Point• Hardness• Luster (shininess)• Odor

Chemical Property

• Chemical Properties can be used to identify a substance…but chemical properties can only be observed when a substance undergoes a chemical change.

• During a chemical change, the composition of matter always changes.

Charcoal

BreakPhysical Change

BurnChemical Change

Chemical Changes

• A chemical change is also called a chemical reaction.– During a chemical reaction, one or more

substances change into one or more new substances.

– Reactant – a substance present at the start of the reaction

– Product – a substance produced in the reaction

Signs of a Chemical Change

• Transfer of energy• Color Change• Production of a gas• Precipitate Formation

Transfer of Energy

• Every chemical change involves a transfer of energy– Energy stored in natural gas is used to cook food. – The methane in the natural gas chemically

combines with oxygen in the air.– Energy is given off in the form of heat and light.– Some of the energy is transferred to and absorbed

by food.

Color Change

When a test strip is dipped in a solution, the color change is used to determine the pH of the solution.

Production of a Gas

Bubbles of carbon dioxide form when two antacid tablets are dropped into a glass of water.

Precipitate Formation

In the production of cheese, a reaction causes milk to separate into solid curds and liquid whey

Physical or Chemical Change?

Signs of a Chemical Change

• If you observe a clue to chemical change, you cannot be certain that a chemical change has taken place. The clue may be the result of a physical change.

• The only way to be sure that a chemical change has occurred is to test the composition of a sample before and after the change.

Law of Conservation of Mass

During any physical change or chemical reaction, the mass of the products is always equal to the mass of the reactants.

Mass of Reactants = Mass of Products

Mass is neither created nor destroyed.

Types of Changes

Physical ChangeProperties change, but the composition of the material does not change

Examples:•Changes of state (solid, liquid, gas) •Changes of size (break, split, grind, cut, crush)

Chemical ChangeChange that produces matter with a different composition

Examples:•Burning•Rusting•Oxidation

Physical or Chemical Change?

• Photosynthesis• Sodium pellet sliced in two• Water heated to steam• Iron rusts• Sugar dissolves in water• Apple rots• Tire is inflated with air• Pancakes cook on a griddle• Food is digested in the stomach