Under the Law of Conservation of Mass, matter cannot be created nor destroyed and only change form. Balancing a chemical equation ensures this law is followed by having the same number of reactant atoms and product atoms.
Examining a Balanced Equation
In a typical balanced equation the numbers in blue are called your coefficients and represent the number of moles for each compound shown.
This written chemical reaction tells us that “2 moles of hydrogen, H2 , react with 1 mole of oxygen , O2 , to produce 2 moles of water, H2O. ”
The numbers in red are the subscripts and combined with the coefficients give us the number of each particular element.
Balancing a Chemical Equation
Just follow our methods for balancing each of the following chemical equations and you’ll be an expert in no time.
For all the equations you will need to set up two lists of elements: one for the reactants and another for the products. If your numerical values in both lists don’t match then you’ll have to balance the chemical equation.
Chemical Equation #1
STEP 1: Set up a list for the elements that are reactants and another list for the elements that are products. The two lists don’t match so we will need to balance the chemical equation.
STEP 2: Start at the top and going down both lists make sure to balance each element one by one.
STEP 3: Balance the number of carbon atoms by placing a “3” in front of CO2. The “3” is distributed so the number of carbon and oxygen atoms are both affected.
STEP 4: Continuing down the lists we next balance the number of hydrogen atoms. We do this by placing a “4” in front of H2O that it distributed to hydrogen and oxygen atom.
STEP 5: Finally balance balance the oxygen atoms by placing a “5” in front of O2.
Chemical Equation #2
STEP 1: Set up your two lists of the elements. Start at the top of the list and work your way down both lists to balance the chemical reaction.
Since both the sodium and chlorine atoms match we continue to the oxygen atoms.
STEP 2: To balance the oxygen atoms we place a “2” in front of NaClO3 and a “3” in front of O2. This gives “6” oxygen atoms on both sides of the chemical equation.
The “2” in front of NaClO3 is also distributed to the sodium (Na) and chlorine (Cl) atoms. This means they will have to be balanced as well.
STEP 3: To balance the sodium (Na) and chlorine (Cl) atoms we place a “2” in front of NaCl.
Chemical Equation #3
At times you will have polyatomic ions (SO42-, NH4+, PO43-) that look the same on both sides of the chemical equation. From the chemical equation we have PO4 on both sides and to make balancing easier just place PO4 in your list of atoms.
STEP 1: We need to balance the calcium atoms by placing a “3” in front of CaBr2. The “3” will be distributed to both the calcium and bromine atoms in CaBr2.
STEP 2: Balance the bromine atoms by placing a “6” in front of LiBr. The “6” will be distributed to both the lithium and bromine atoms.
STEP 3: Balance the lithium and PO4 atoms by placing a “2” in front of Li3PO4.
Chemical Equation #4
STEP 1: The lead (Pb) atoms match so we continue to the oxygen atoms.
The lead (Pb) atoms match so we continue to the oxygen atoms.
STEP 2: Balance the oxygen atoms by placing a “2” in front of H2O. The “2” will be distributed to both the hydrogen and oxygen atoms.
STEP 3: Balance the hydrogen and iodine atoms by placing a “2” in front of HI.