Dr Pusey

www.puseyscience.com

Physical Changes

• Do not create new substances

• Often reversible

• Four main types of physical change

1. Change of state

2. Change of shape

3. Expansion (getting bigger) or contraction (getting smaller)

4. Mixing together, dissolving

Examples

Solid ice melting into a liquid

Wood being chopped up, changing shape

Tablet dissolving in water

Chemical Changes

• Creates new substances

• Often not reversible

• Four main types of chemical change

1. Colour change

2. Making a gas – see bubbles, smell

3. Making a new solid (sometimes called a precipitate)

4. Releasing or absorbing energy

Examples

Fireworks releasing heat and light energy

A nail getting rusty (rust = new solid)

Chemical Reactions Chemical reactions require REACTANTS and create

PRODUCTS

Reactants are the chemicals that are combined together to form the Products

We write worded chemical equations like this:(combusting Hydrogen – POP TEST!)

Hydrogen + Oxygen Water

ProductsReactants

Chemical Equations Chemical equations can be used to represent many of the

processes around us

Photosynthesis: Plants convert water and carbon dioxide to create Oxygen and Sugar:

Carbon Dioxide + Water Glucose (sugar) + Oxygen

1) What are the reactants in this reaction? What are the products?

2) If the formula for Glucose is C6H12O6, could you write the chemical equation with symbols?

Endothermic or ExothermicCO2+ H2O C6H12O6 + O2

Chemical reactions can be exothermic or endothermic

Endothermic: The reaction absorbs energy

Exothermic: The reaction gives off energy

3) Is Photosynthesis an exothermic or endothermic reaction?

Conservation of MassMass cannot be created or destroyed in a reaction. Therefore, the mass of the reactants must equal the mass of the products.

Translation: The number of each type of atom on each side of the equation must be the same. This makes the equation Balanced.

Hydrogen + Oxygen Water

H2 + O2 H2O

4) How many Hydrogen and Oxygen atoms on each side of the equation?

5) Is this equation balanced?

Balancing EquationsEquations can be balanced by putting numbers (coefficients)

at the front of the formula which multiplies the number of every atom in that formula:

2H2 + O2 2H2O

Now answer:

6) How many Hydrogen and Oxygen atoms on each side of the equation?

7) Is this equation balanced?

Balance PhotosynthesisCO2+ H2O C6H12O6 + O2

8) (HARD) This equation isn’t balanced. Try to balance it!

Hint: Balance one element at a time, start with Carbon.

Your Turn:9) Copper and Sulphur Dioxide are combined in a reaction which forms copper sulphide and oxygen gas.

10) Our respiration (breathing) forms a reaction of Glucose (sugar) and Oxygen gas, which forms Carbon Dioxide and Water (vapour)

STEPS: Identify the reactants and products Write a word equation Write an unbalanced formula equation Balance the equation