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AQA GCSE Chemistry Equations

Equations

This page covers the following topics:

1. Chemical reactions
2. Balancing equations
3. Half equations
4. Ionic equations

Equations are used to describe chemical reactions in terms of their reactants and products. They can be written as either a word equation or by using the correct formulae.

Chemical reactions

For equations to be chemically correct, they have to be balanced. This requires both sides of the equation to have the same charge and the same number of atoms of each element.

Balancing equations

Half equations are a type of ionic equation that represent either an oxidation (loss of electrons) or a reduction (gain of electrons). Like all equations, they need to be balanced. First you balance the atoms, adding water if you're missing oxygen or H+ if you're missing hydrogen. Then you balance the charges by adding electrons.

Half equations

Ionic equations show which ions interact directly in a chemical reaction and which are spectator ions. All aqueous, ionic compounds are split into their respective ions to form the full ionic equation. Then the spectator ions are cancelled out to create the net ionic equation. Half equations can be combined to create redox equations for a chemical reaction, but the number of electrons in each half equation must be the same. This can be achieved by multiplying the entire half equation.

Ionic equations

1

Solid copper and sulphur react together to form copper (II) sulphide. Write the word equation and corresponding chemical formula equation for this reaction.

Solid copper and sulphur react together to form copper (II) sulphide. Write the word equation and corresponding chemical formula equation for this reaction.

2

Combine the two half-equations to determine the redox equation.

Clβ‚‚ + 2e⁻ β†’ 2Cl⁻
Fe²⁺ β†’ Fe³⁺ + e⁻

Combine the two half-equations to determine the redox equation. 

Clβ‚‚ + 2e⁻ β†’ 2Cl⁻ 
Fe²⁺ β†’ Fe³⁺ + e⁻

3

Balance and combine the two half-equations to determine the redox equation.

Balance and combine the two half-equations to determine the redox equation.

4

Calcium carbonate reacts with hydrochloric acid to produce water, calcium chloride and carbon dioxide gas. Write the chemical formula equation for the process described.

Calcium carbonate reacts with hydrochloric acid to produce water, calcium chloride and carbon dioxide gas. Write the chemical formula equation for the process described.

5

Write the balanced net ionic equation for the reaction of zinc nitrate and potassium carbonate.

Write the balanced net ionic equation for the reaction of zinc nitrate and potassium carbonate.

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