5.5 Types of Reactions There are some general patterns among all reactions that help us classify reactions as one of the following: Combination Decomposition Single Replacement Double Replacement

Combination Reactions In a combination reaction, two or more elements or compounds bond to form one product. A + B → AB Examples: S + O 2 → SO 2 2Mg + O 2 → 2MgO

Decomposition Reactions In decomposition reaction, a reactant splits into two or more simpler products. Usually heat or some other physical action is required for this to happen AB → A + B For example, when mercury(II) oxide is heated, the compound breaks apart into mercury atoms and oxygen 2HgO → 2Hg + O 2

Replacement Reactions In a replacement reaction, elements in a compound are replaced by other elements. In a single replacement reactions, a reacting element switches place with an element in the other reacting compound A + BC → AC + B Example Zn + 2HCl → ZnCl 2 + H 2

More replacement reactions In a double replacement reaction, the positive ions in the reacting compounds switch places. AB + CD → AD + CB Example BaCl 2 + Na 2 SO 4 → BaSO 4 + 2NaCl