Different types of chemical reaction I

two or more substances combine together, to form a single substance. This type of reaction is called a combination or a synthesis, and it has only one product. One example is the reaction between iron and sulphur, that you met on page 64  

In some reactions, a single substance breaks down into two or more simpler substances. This is called decomposition. A decomposition reaction has only one reactant. An example is the decomposition of calcium carbonate or limestone  

The label on the arrow shows that the limestone must be heated, to make it decompose. Decomposition caused by heat is called thermal decomposition. 

Some decomposition reactions are caused by light. For example silver chloride is a white solid. It breaks down in light to give tiny black crystals of silver  

In cement works, limestone is decomposed to quicklime and used to make cement. The decomposition is carried out in rotating kilns. There are five of them at the front of this photograph. 

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