1. 3.3 Physical and Chemical Changes

2. 3.3 Physical Changes
In physical changes, the appearance of a substance changes, but the chemical bonds holding the substance together do not change.
Examples: melting, freezing, boiling, dissolving
Ex. When salt and sugar dissolve in water it is a physical change. The chemical makeup of the salt and sugar are not changed.

3. Chemical Changes
In chemical changes, new substances are produced in the process of breaking chemical bonds and forming new ones.
You start with the substances that are going to react. These substances are called reactants. The new substances produced are called products.

4. What are the reactants and what is the product?

5. How do you know a chemical reaction has taken place?
Think about:
Gas is produced and makes bubbles.
the colour
The colour has changed
gas
The protein in the egg becomes firmer when it is cooked.
the egg

6. How do you know which are the reactants?
When do you use them?
Think about:
They react with each other to make something new
They are used at the beginning of a chemical reaction
What happens to them?

7. How would you write an equation for making a cake?
Discuss with your partner. You will need to use all these words and symbols. +
butter
cake + +
eggs
flour
sugar

8. Which are the reactants and products?
Spend a few minutes underlining the reactants and circling the products on your sheet
When you are ready, compare your answers with your partner and discuss what you have written
Phrases you could use:
It must be the reactant /
product because…
I think it’s the reactant/product because…
It’s the reactant/product because….

9. Which are the reactants?
Mike took methane and burnt it in oxygen. This produced carbon dioxide and water.
Iron sulphate is formed when iron is added to sulphuric acid. Hydrogen gas is also given off.
Pupils found that sodium chloride and water were formed when sodium hydroxide was added to hydrochloric acid.
4. If you add nitric acid to sodium carbonate they will react together and produce sodium nitrate, carbon dioxide and water.

10. Which are the reactants?
Mike took methane and burnt it in oxygen. This produced carbon dioxide and water.
Iron sulphate is formed when iron is added to sulphuric acid. Hydrogen gas is also given off.
Pupils found that sodium chloride and water were formed when sodium hydroxide was added to hydrochloric acid.
4. If you add nitric acid to sodium carbonate they will react together and produce sodium nitrate, carbon dioxide and water.

11. Which are the products?
Mike took methane and burnt it in oxygen. This produced carbon dioxide and water.
Iron sulphate is formed when iron is added to sulphuric acid. Hydrogen gas is also given off.
Pupils found that sodium chloride and water were formed when sodium hydroxide was added to hydrochloric acid.
4. If you add nitric acid to sodium carbonate they will react together and produce sodium nitrate, carbon dioxide and water.

12. Which are the products?
Mike took methane and burnt it in oxygen. This produced carbon dioxide and water.
Iron sulphate is formed when iron is added to sulphuric acid. Hydrogen gas is also given off.
Pupils found that sodium chloride and water were formed when sodium hydroxide was added to hydrochloric acid.
4. If you add nitric acid to sodium carbonate they will react together and produce sodium nitrate, carbon dioxide and water.

13. The chemical equations (grade 10)
methane + oxygen  carbon dioxide + water
2. iron + sulphuric acid  iron sulphate + hydrogen
3. sodium hydroxide + hydrochloric acid  sodium chloride + water
4. nitric acid + sodium carbonate  sodium nitrate + carbon dioxide + water.

14. Chemical Changes Evidence of chemical change: Colour change
Heat, light, sound produced or consumed
Bubbles of gas form
Formation of a precipitate (solid formed from 2 liquids)
The change is difficult to reverse

15. Energy Changes
In both physical and chemical changes, energy changes take place. This energy change can mean releasing energy to or absorbing energy from the environment.
See page 99

16. Energy Changes Exothermic reactions involve
the overall release of energy
in the form of heat and light.
Memory Tip:
Exo – starts with the letters “ex” similar to exit
Endothermic reactions involve the overall absorption of energy.
Endo – starts with the letters “en” similar to enter

17. Applications of Chemical Changes
Some chemical changes present problems, while others provide opportunities and advantages.
Corrosion is a major problem for steel structures.
By protecting steel surfaces, the chemical reaction of iron with oxygen can be prevented.

18. Applications of Physical and Chemical Changes
First Nations people of
the Pacific Coast have
used drying and smoking
as a means of preserving food.
Drying is a physical change that removes water from the cells of the fish and bacteria which prevent the bacteria from attacking the meat.
Smoke causes chemical
changes in meat that
kill bacteria.