# Balancing Chemical Equations

In these lessons, we will look at some examples of balancing chemical equations containing polyatomic ions.

Atoms can neither be destroyed nor created during a simple chemical reaction. Therefore, in a chemical reaction,
The sum of atoms before reaction = the sum of atoms after reaction

The following figure gives some hints on how to balance chemical equations. Scroll down the page for more examples and solutions. ### General Rules for balancing chemical equations – Polyatomic Ions

Balancing chemical equations may require some trial and error. There are some general rules that could be helpful, but they may not work all the time.

Rule 1
Balancing chemical equations using the one’s and two’s technique

Rule 2
Balancing chemical equations using the two’s and three’s technique

Rule 3
Balancing chemical equations using the CHO technique

Rule 4
Balancing chemical equations using the even technique

Rule 5
Balancing chemical equations containing polyatomic ions

Case 1: If the polyatomic ion remains the same before and after the reaction, then treat it as “a single element” for ease of calculation. Try to start with the most complicated-looking group.

Example:
Balance the equation

Ca + HNO3 → H2 + Ca(NO3)2

Solution:

• The nitrate ion NO3 is unchanged before and after the reaction.
• There is one NO3 on the left and two on the left.
• Using the one’s and two’s technique, the equation is balanced by placing the coefficient of 2 for HNO3 Ca + 2HNO3 → H2 + Ca(NO3)2
• We test the other atoms and we find that we already have a balanced equation.
• Check to make sure that all coefficients are in the lowest-possible ratio

How to balance chemical equations containing polyatomic ions?

Example:
Balance the following equation:
Ca(NO3)2 + Na2S → CaS + NaNO3

Example:
Balance the following chemical equation:
Fe(NO3)3 + (NH4)2CO3 → Fe2(CO3)3 + NH4NO3

Example:
Balance the following chemical equation:
AgNO3 + K2CrO4 → Ag2CrO4 + KNO3

How to balance chemical equations containing polyatomic ions?

Example:
Balance the following chemical equation:
Pb(NO3)2 + NA2CO3 → PbCO3 + NaNO3

Case 2: If the polyatomic ion is changed after the reaction then it would be necessary to consider each atom individually.

Example:
Balance the chemical equation

Ba(OH)2 + H3PO4 → BaHPO4 + H2O

Solution:

• Use the CHO technique. Since we don’t have carbon, we could try to balance the hydrogen first.
• We have five hydrogen atoms on the left and three hydrogen atoms on the right.
• To balance the hydrogen, we can place the coefficient of 2 at H2O Ba(OH)2 + H3PO4 → BaHPO4 + 2H2O
• We test the other atoms and we find that we already have a balanced equation.
• Check to make sure that all coefficients are in the lowest-possible ratio.

How to balance chemical equations with polyatomic ions by rewriting H2O as H(OH)?

Examples:
Balance the following chemical equations:
Al4C3 + H2O → Al(OH)3 + CH4
C3H8 + O2 → CO2 + H2O
C6H6 + O2 → CO2 + H2O

Three helpful tips and tricks that make Balancing Chemical Equations easier

Tip #1: Put a star(*) next to any element appearing more than once on either the product or the reactant side; balance those elements last.
Tip #2: Recognize polyatomic groups that appear on both sides of the equation, and tea them as single items (e.g. don’t break SO4 into one sulfur and four oxygens)
Tip #3: If you have H and OH on one side and H2O on the other, it is helpful to rewrite H2) as H(OH).

Examples:
Balance the following chemical equations:

1. C3H8 + O2 → CO2 + H2O
2. Al2(SO4)3 + Ca(OH)2 → Al(OH)3 + CaSO4
3. H3PO4 + NaOH → Na3PO4 + H2O

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