Write the balanced molecular equation for each reaction and the net ionic equation?

1 Answer
Feb 25, 2016

The balanced equation is necessary to ensure that all elements have been accounted for in the reaction. The net ionic reaction is a simplified form of the balanced equation that ONLY includes those elements that are actually changing chemical links or oxidation states.


To balance a chemical reaction you need to know the likely combinations of elements. Once you have the basic equation with reactants (given in this problem) and products (deduced from oxidation states, or looked up in a reference) you need to make sure that equal numbers of each element are on each side of the equation. That is “balancing” the equation.

a) #(NH_4)_3PO_4 + LiOH → NH_4OH + Li_3PO_4#
In this case there are 3 N, 13 H, 5 O, 1 P and 1 Li on the reactant side, and 1 N, 5 H, 5 O, 1 P and 3 Li on the production side. A combination of reactants and products must be found to make the values of each element equal on both sides. Balance the #NH_4# unit first, then the OH, and the Li and P should confirm a correct balance.

b) Al + MgS → #Al_2S_3# + Mg
Here we have 1 Al, 1 Mg and 1 S on the reactant side, and 2 Al, 3 S and 1 Mg on the product side. Both are 'keyed' to the S element, so balancing the reactant MgS with the product S_3 first, then balancing the Al and Mg one each side will be straightforward.

c) # Al + ZnNO_3 → Al(NO_3)_3 + Zn#
This one is fairly simple, with only 1 Al, 1 Zn, 1 N and 3 O on the reactant side, and 1 Al, 3 N, 9 O and 1 Zn on the product side. Noting that #NO_3# is a unit on each side, we only need to increase the reactant side to 3 #ZnNO_3# units and balance the product side with 3 Zn.