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Fireworks are an example of a chemical reaction.

Chemical Reactions

Chemical reactions rearrange atoms into new substances. Practise writing and balancing equations, spotting reactants and products, and using state symbols and coefficients accurately.

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Fascinating Fact:

Chemical equations use symbols and formulas to show reactants and products. Balancing an equation ensures the same number of each atom on both sides.

In GCSE Chemistry, chemical reactions are described using word equations and symbol equations. You learn how atoms are conserved, how to choose correct formulae, and how coefficients show the ratio of reactants to products.

Key Terms

Reactant: A substance that is used up in a chemical reaction.
Product: A new substance that is made in a chemical reaction.
Coefficient: The number in front of a formula that shows how many units take part, for example 2H₂.

Frequently Asked Questions (Click to see answers)

What is a chemical equation in GCSE Chemistry?

A chemical equation is a line of symbols that shows which reactants change into which products. It uses chemical formulae and an arrow to show the direction of the reaction.

How do you balance chemical equations step by step?

To balance an equation, count each type of atom on both sides, then change only the coefficients until the totals match. Do not change the small numbers inside a formula because that would change the substance.

What do (s), (l), (g) and (aq) mean in chemical equations?

These are state symbols: (s) solid, (l) liquid, (g) gas and (aq) dissolved in water. They give extra information about the substances during the reaction.

Try These Related Quizzes

1 .

What is the only reaction that removes carbon dioxide from the atmosphere naturally?

Decomposition

Combustion

Respiration

Photosynthesis

All the other reactions here put carbon dioxide into the atmosphere

2 .

What reaction is occurring when decane is split into ethene and octane?

Cracking

Polymerisation

Reduction

Neutralisation

Long chain hydrocarbons are split into shorter chain hydrocarbons by cracking

3 .

What type of reaction occurs when hydrocarbons burn in an insufficient supply of oxygen?

Combustion

Incomplete combustion

Reduction

Thermal decomposition

As there is not enough oxygen for complete combustion, the process is incomplete

4 .

What type of reaction is shown in the symbol equation?
Fe₂O₃ + 3CO → 2Fe + 3CO₂

Oxidation

Combustion

Reduction

Decomposition

OK, technically, there is an oxidation too, but you should have recognised this as being one of the reactions in the blast furnace which has the iron as its focus so at this level, this equation shows the reduction of iron oxide to iron by the removal of oxygen

5 .

What type of reaction occurs when limestone (calcium carbonate) is heated and becomes calcium oxide?

Oxidation

Reduction

Thermal decomposition

Combustion

Themal = heat, decomposition = break down

6 .

What reaction is involved in the hardening of vegetable oils?

Polymerisation

Cracking

Hydrogenation

Setting

Hydrogenation involves adding hydrogen to vegetable oils to harden them

7 .

What type of reaction occurs at the positive electrode when copper sulfate is electrolysed using copper electrodes?

Oxidation

Reduction

Combustion

Decomposition

Copper atoms lose electrons to the positive electrode to become copper ions which go into solution (remember LORG - Loss of electrons is Oxidation, Reduction is a Gain of electrons)

8 .

What reaction is involved in the production of poly(ester)?

Cracking

Polymerisation

Decomposition

Neutralisation

Polymers are formed from many monomers. Monomers is a general term describing any small and reactive molecules that can be joined together to form a polymer

9 .

What type of reaction is shown by the following word equation?
Hydrochloric acid + sodium hydroxide → sodium chloride + water

Decomposition

Displacement

Neutralisation

Combustion

Acid + alkali is a neutralisation reaction

10 .

What type of reaction does the following word equation describe?
Magnesium + zinc chloride → magnesium chloride + zinc

Oxidation

Reduction

Thermal decomposition

Displacement

Magnesium is more reactive than zinc and so displaces it from a compound

You can find more about this topic by visiting BBC Bitesize - Chemical changes

Author: Kate Gardiner (Chemistry Educator & GCSE Quiz Writer)

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