A decomposition reaction is a type of chemical reaction in which a compound breaks down into simpler substances. This process can occur when a compound is heated, exposed to light, or comes into contact with a catalyst. Decomposition reactions are often used in industrial processes to break down complex compounds into more useful substances.

A decomposition reaction is the opposite of a combination reaction, which is a chemical reaction in which two or more substances combine to form a new compound.

The general formula for a decomposition reaction is:

```

AB → A + B

```

where AB is the compound that is breaking down, and A and B are the simpler substances that are formed.

Here are some examples of decomposition reactions:

* When water (H2O) is heated, it breaks down into hydrogen (H2) and oxygen (O2):

```

2H2O → 2H2 + O2

```

* When calcium carbonate (CaCO3) is heated, it breaks down into calcium oxide (CaO) and carbon dioxide (CO2):

```

CaCO3 → CaO + CO2

```

* When potassium chlorate (KClO3) is heated, it breaks down into potassium chloride (KCl) and oxygen (O2):

```

2KClO3 → 2KCl + 3O2

```

Decomposition reactions can also be caused by light or by the presence of a catalyst. For example, when silver chloride (AgCl) is exposed to light, it breaks down into silver (Ag) and chlorine (Cl2):

```

2AgCl → 2Ag + Cl2

```

Decomposition reactions are also used industrially to produce a variety of substances, including hydrogen, oxygen, and carbon dioxide.