Chemical Reactions
Science: KS3, topic 2.2.1
Chemical Reactions
A chemical reaction is when the atoms in an element or compound are rearranged and connected together in a different way.
Chemical reactions
- In a reaction, the substances you have at the start are called the reactants.
- The reactants' atoms are broken apart and then reconnected in a different order to make something new.
- The new substances are called the products.
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Equations
- Each element or compound can be represented either by a word or a formula (symbols).
- There are two types of chemical equations: word equations and symbol equations.
- A chemical equation is always shown with the reactants on the left of an arrow and the products on the right.
- E.g. reactants → products
Equations
- If there is more than one reactant or product, then they are written with '+' signs between them.
- There can be any number of reactants or products - it all depends on the chemicals involved.
- It is important to remember that the little number in a formula tells you how many of each atom you have and that the little number goes on the right of an atom.
Examples
- Water:
- Word equation: oxygen + hydrogen → water
- Symbol equation: O2 + 2H2 → 2H2O
- Burning methane:
- Word equation: methane + oxygen → water + carbon dioxide
- Symbol equation: CH4 + 2O2 → H2O + CO2
Test yourself on Chemical Reactions
What is the correct word equation for the burning of methane?
Which of these are true of a chemical reaction?
In the equation CH4 + 2O2 → H2O + CO2, how many atoms of each element are in one molecule of CO2?