Year 8 Science Lesson

Physical and Chemical Change

Year 8 Science

Ms Alexander

Physical Change ?

Definition of a PHYSICAL CHANGE

A physical change occurs when a a substance changes but no new substance is formed.

Example of a PHYSICAL CHANGE?

Melting of ice to water

Chewing my breakfast

Chemical Change ?

Definition of a CHEMICAL CHANGE

A chemical change occurs when a new substance is formed. Another word for Chemical Change is CHEMICAL REACTION.

Example of a CHEMICAL REACTION?

Cooking a cake

Burning toast

What are products and reactants?

Chemical Reactions ?

There are 4 types of CHEMICAL REACTIONS Combination

Break-down

Precipitation

Combustion

Last Class

What pracs did you do?

What happened? What was the result?

Combination Reaction ?

Definition: A combination reaction occurs when two reactants combine to form a single new substance

Breakdown Reaction ?

Definition: A Breakdown reaction occurs where one substance breaks up to a number of smaller ones.

Decomposition in your compost heap!Start with: Plant material--> C

Precipitation Reaction?

Definition: A reaction were a solid is produced when two solutions are added together.

Combustion Reaction ?

Definition: A combustion reaction occurs when a compound reacts with oxygen to produce carbon dioxide and energy.

Example Fireworks, a Bunsen burner, Human respiration

Compare and Contrast ?

Create a Venn Diagram. Use the words: products, reactant, synthesis, decomposition

Combination Breakdown Reaction

What might we do to change how quickly a reaction occurs?

amount of reactants or concentrations

Temperature (reactants travel faster)

surface area (ball with sticks)

helper chemicals (catalyst)

Rate of Reaction ?

A Rate of Reaction is the speed at which new products are formed.

On a new page.... ?

What effects the rate of a chemical reaction?

Surface Area

Temperature

Concentration

Catalysts

Surface area?

A increase of surface area means that there is more rates of contact between reactants

Cut and paste

Temperature?

A increase of temperature means that the reactants can move faster and have more energy to breakdown bonds

What happens if we decrease the energy?

Concentration of reactants?

The more reactants in a reaction the more products are produced.

Cut and paste

What happens if we remove reactants?

Catalysts?

Catalysts are special helper chemicals that assist molecules to react. But they do not combine with reactants.

Example: Catalytic Converter Movie

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