Single-displacement reactions occur when one element replaces another element in a compound. The general form of a single-displacement reaction is:

```

A + BC → AC + B

```

In this reaction, element A replaces element B in compound BC to form compound AC and element B. For example, when iron metal is placed in a copper sulfate solution, the iron replaces the copper in the compound to form iron sulfate and copper metal:

```

Fe + CuSO₄ → FeSO₄ + Cu

```

Double-displacement reactions occur when two compounds exchange ions to form two new compounds. The general form of a double-displacement reaction is:

```

AB + CD → AD + CB

```

In this reaction, ions A and B from compound AB exchange with ions C and D from compound CD to form two new compounds, AD and CB. For example, when sodium chloride (NaCl) is mixed with silver nitrate (AgNO₃), the sodium ions (Na⁺) from the sodium chloride compound exchange with the silver ions (Ag⁺) from the silver nitrate compound to form sodium nitrate (NaNO₃) and silver chloride (AgCl):

```

NaCl + AgNO₃ → NaNO₃ + AgCl

```

The main difference between single- and double-displacement reactions is the number of elements that are replaced. In a single-displacement reaction, one element replaces another element, while in a double-displacement reaction, two elements exchange ions to form two new compounds.