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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