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Chemical Reaction

(Redirected from React)

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.

Signs of Chemical Reactions

There are three signs that a chemical reaction is taking place:

  • A colour change.
  • A temperature change.
  • Effervescence (bubbles of gas are given off.

Examples

These are two examples of Combustion

RearrangeAtoms1.png

Hydrogen + OxygenWater

2H2 + O2 → 2H2O

RearrangeAtoms2.png

Methane + OxygenWater + Carbon Dioxide

CH4 + 2O2 → 2H2O + CO2

Types of Chemical Reaction

Key Stage 4

Meaning

A Chemical Reaction is when the atoms in molecules break their bonds and form new bonds, usually with other atoms.

About Chemical Reactions

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.

There are three ways that chemical reactions can happen:

References

AQA

Chemical reaction, page 108, GCSE Physics; Student Book, Collins, AQA

OCR

Chemical reactions, pages 27, Gateway GCSE Physics, Oxford, OCR

Beyond the Curriculum