Reactions

Question 1

How can you tell if a chemical reaction has occurred?

Answer 1

We know a chemical reaction has happened because new substances are produced.
Compounds react by mixing with other chemicals or using heat or light.
A chemical reaction has occurred if there is a colour given off.
Chemical reactions also involve an energy change usually as heat or light e.g. Combustion.

Question 2

What happens in a chemical reaction?

Answer 2

A new substance is formed.

Usually it’s irreversible.

Question 3

How do reactions take place?

Answer 3

Some reactions just mix substances.
If mixing two liquids makes a solid it is called precipitate.
Some reactions need energy e.g. Heat, light and electricity.
When energy splits up compounds it’s called decomposition.

Question 4

Explain the word equation for a chemical reaction?

Answer 4

You start with the reactants.
You end up with the products.
Magnesium + oxygen ( the reactants ) make magnesium oxide ( the product )

Question 5

What happens in a physical change?

Answer 5

Melting, evaporating, Condensing and freezing are examples of physical change.
In physical change no new substance is formed.
E.g. Ice melts to water evaporates to steam condenses to water freezes to ice.

Question 6

What are mixtures?

Answer 6

Elements and compounds can be mixed together.
Mixtures are easier to separate than the elements in a compound.
Naturally occurring mixtures e.g. Soil, river water and sea water.

Question 7

What are the differences with mixtures?

Answer 7

Mixtures no fixed melting and boiling point.
Elements and compounds do.
Air is a mixture of gasses mostly nitrogen and oxygen.
Gasses in the air are separated by fractional distillation.