C. Single Replacement:

• a more active element takes the place of another element in a compound and sets the less active one free.
• Basic form: A  +  BX  -->    AX  +  B  or  AX  +  Y  -->    AY + X

Examples of replacement reactions:

1. Replacement of a metal in a compound by a more active metal.

Ex. Fe_(s)  +  CuSO_4(aq)  -->    FeSO_4(aq)  +  Cu_(s)

2. Replacement of hydrogen in water by an active metal.

Ex. 2Na_(s)  +  2H₂O_(l)  -->    2NaOH_(aq)  +  H_2(g)

3. Replacement of hydrogen in acids by active metals.

Ex. Zn_(s)  +  2HCl_(aq)  -->    ZnCl_2(aq)  +  H_2(g)

4. Replacement of nonmetals by more active nonmetals.

Ex. Cl_2(g)  +  2NaBr_(aq)  -->    2NaCl_(aq)  +  Br_2(l)

NOTE: Refer to the activity series for metals and nonmetals to predict products of replacement reactions. If the free element is above the element to be replaced in the compound, then the reaction will occur. If it is below, then no reaction occurs.