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Writing Chemical Equations
Ionic Equations
More lessons on Chemistry
In these lessons, we will look at some examples of balancing chemical equations containing polyatomic ions.
Balancing chemical equations is a fundamental skill in chemistry that ensures the Law of Conservation of Mass is upheld. This law states that matter cannot be created or destroyed in a chemical reaction. Therefore, the number of atoms of each element must be the same on both sides of a chemical equation.
The sum of atoms of each element before reaction = the sum of atoms of each element after reaction
The following figure gives some hints on how to balance chemical equations. Scroll down the page for more examples and solutions.
How to balance a chemical equation
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:
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:
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:
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