The Chemical reaction reference article from the Simple Wikipedia on 24-Jul-2004
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Chemical reaction

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A Chemical reaction occurs when one or more chemicals are converted into one or more other chemicals. Examples include:

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 you make it hot it starts to burn.

Some reactions give out energy. These are called exothermic. For other reactions you must put in energy to make them happen. These are called endothermic.

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