# Chemical reaction

Rusting iron
A bonfire is an example for redox.

A chemical reaction happens when one or more chemicals are changed into one or more other chemicals. Examples:

Some reactions are very fast, and others are very slow. Some happen at different speeds, depending on temperature or other things. For example, wood does not react with air when it is cold, but if it is made hot enough, it will start to burn. Other reactions such as Nuclear Reactions differ in the way that Nuclear Reaction does not need a catalyst. They also cannot be stopped, sped up or slowed down.

Some reactions give out energy. These are called exothermic. In other reactions, energy is taken in. These are called endothermic.

## The Five Common Types of Reactions

1. Synthesis Reactions
2. Decomposition Reactions
3. Single Replacement Reactions
4. Double Replacement Reactions
5. Combustion Reactions

## Equations

A chemical reaction is being displayed by an equation:

$\mathrm{ A + B \longrightarrow C + D}$
Here, A and B react to C and D in a chemical reaction.

## Example

This is an example of a combustion reaction.

$\mathrm{C + O_2 \longrightarrow CO_2}$

carbon + oxygencarbon dioxide