PREDICTING WHETHER A SINGLE REPLACEMENT REACTION WILL OCCUR

The reactants in a single replacement reaction are an element (by itself) and a compound.  Some single replacement reactions will happen, others will not.  In order to determine if a single replacement reaction will occur, you must use the Activity Series.  (It is located on page 7 of the Reference Tables, but I have included one here so you don’t have to go searching for it.)

# ACTIVITY SERIES OF METALSLi                         Rb                         K                         Ba                         Sr                         Ca                         Na                                            Replace hydrogen from cold water ---------------------------------------------------------------------------------------------------------------------                         Mg                         Al                         Mn                         Zn                         Cr                         Fe                         Cd                                            Replace hydrogen from steam --------------------------------------------------------------------------------------------------------------------                         Co                         Ni                         Sn                         Pb                         H2                                             Replace hydrogen from acids --------------------------------------------------------------------------------------------------------------------                         Sb                         Bi                         Cu                         Hg                                            React with oxygen to form oxides --------------------------------------------------------------------------------------------------------------------                         Ag                         Pt                         Au

EXAMPLE 1 – Will the following reaction happen or not?                               Al  +  PbCl2 à

Step 1 – Look at the element by itself.  Is this element a metal or a nonmetal?  Al (aluminum) is a metal because it is located to the left side of the staircase line on the Periodic Table.
Step 2 – You will compare the type of element by itself to the similar type of element in the compound.  In this case, aluminum is a metal, so I will compare it with the metal in the compound (which is Pb).

Step 3 – RULE:  The element that is by itself must be HIGHER on (closer to the top of) the Activity Series for the reaction to happen!  In this case…

Al         (by itself)
Mn
Zn
Cr

Fe
Cd                                            Replace hydrogen from steam
--------------------------------------------------------------------------------------------------------------------
Co
Ni
Sn
Pb         (in compound)

Aluminum (Al) is higher than lead (Pb), so the reaction happens.

What are the products of the reaction?

Aluminum and lead “switch places”.  However, remember to use the oxidation numbers of the elements to write the formulas.  Then, balance the equation.

Al  +  PbCl2  à  Pb  +  AlCl3                   (aluminum has a +3 oxidation number)

Balanced…         2 Al  +  3 PbCl2  à  3 Pb  +  2 AlCl3

EXAMPLE 2 – Will the following reaction happen or not?                               Fe + Mg(NO3)2  à

Answer:  Iron (Fe) needs to be higher on the Activity Series than magnesium (Mg) in order for the reaction to occur.  It is not, so there is no reaction.

EXAMPLE 3 – Will the following reaction happen or not?                               NaCl  +  Br2  à

Answer:  Br2 is the element by itself.  It is a nonmetal, so I have to compare it to the nonmetal in the compound – which is Cl.  Br needs to be higher than Cl in order for the reaction to happen.  It is not, so there’s no reaction.

EXAMPLE 4 – Will the following reaction happen or not?                               AlBr3  +  F2  à

Answer:  F2 is the element by itself.  It is a nonmetal, so I have to compare it to the nonmetal in the compound – which is Br.  F needs to be higher than Br in order for the reaction to happen.  It is, so the reaction happens.  Fluorine and bromine “switch places”.  Remember to use the oxidation numbers of the elements to write the formulas.  Also, remember that fluorine, chlorine, bromine, and iodine are DIATOMIC – that means that these elements will have a subscript of 2 when they are by themselves.

AlBr3  +  F2  à  Br2  +  AlF3

Balanced…         2 AlBr3  +  3 F2  à  3 Br2  +  2 AlF3

Here are a few for you to try…

1.         Al  +  NiBr2  à
2.         Fe2(SO4) 3  +  Ag
à
3.         NaCl  +  F2
à
4.         Ba(NO3) 2  +  Ni
à
5.         I2  +  AlBr3
à
6.         Ca  +  KCl
à
7.         Mg  +  Zn3(PO4) 2
à
8.         Na  +  SnCO3
à