What type of chemical reaction is the example below?
Na2S + HCl -> NaCl + H2S

In a double replacement reaction two species (typically ions) are replaced (AB + CD -> AD +CB). The other common types of chemical reactions are:
- Decomposition: single compound breaks down into two or more simpler substances (AB -> A + B).
- Single Replacement more active element replaces less active element (A + BC -> B + AC).
- Combustion (burning) - a compound (typically carbon) combines with oxygen in the air.