Combination Reactions

There are many pairs of reactants which combine to give a single product. The reactions happen when it is energetically favorable to do so. Examples are

Decomposition Reactions

Many molecules which are stable at room temperature will decompose upon being heated.

Single Substitution Reactions

When a reaction involves an element which displaces another in a compound, it is called a single substitution or single replacement reaction. The name "displacement reaction" is also used. For example, a copper strip dipped in a silver nitrate solution will displace silver atoms, producing copper nitrate and precipitating silver metal crystals.

If zinc metal is dipped into an acid, the zinc will displace the hydrogen from the acid.

Generally, active metals will displace hydrogen from an acid.

Double Substitution Reactions

When a reaction appears to exchange parts of the reactants, the reaction is referred to as a double substitution or double replacement reaction. Another name used for such reactions is "metathesis reactions". When the reactants are ionic compounds in solution, the anions and cations of the compounds are exchanged. Probably the most famous of such reactions among teachers of chemistry is the reaction between lead nitrate and potassium iodide:

Both of the reactants form colorless solutions, but the lead iodide product is a dramatic yellow solid which precipitates out of the solution.