Chemical Reaction
Contents
Key Stage 2
Meaning
A chemical reaction is when one substance changes into another.
About Chemical Reactions
- Most chemical reactions are irreversible.
- Chemical reactions usually cause a change in temperature.
- Chemical reactions you should know are:
Key Stage 3
Meaning
A Chemical Reaction is when the atoms in molecules break their bonds and form new bonds, usually with other atoms.
About Chemical Reactions
- Most chemical reactions are irreversible.
- In a chemical reaction the atoms rearrange to form a new substance.
- Chemical reactions often need some energy to start, like combustion where the fuel needs to be heated to start.
- If a chemical reaction gives off more energy than it needs to start then it is called an exothermic reaction. In these reactions the temperature increases.
- If a chemical reaction takes in more energy than it gives out then it is called an endothermic reaction. In these reactions the temperature decreases.
Examples
These are two examples of Combustion
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2H2 + O2 → 2H2O |
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Methane + Oxygen → Water + Carbon Dioxide CH4 + 2O2 → 2H2O + CO2 |
Types of Chemical Reaction
- Combustion - A chemical burns in the presence of Oxygen.
- Thermal Decomposition - A compound breaks down into smaller compounds.
- Oxidation - A chemical reacts with Oxygen.
- Displacement Reaction - One element replaces another in a compound.
- Neutralisation - An acid and a base react to make a salt.