Balancing Chemical Equations

A chemical equation identifies the starting and finishing chemical as reactants and products:

Reactants à Products

C₃H₈ + 5O₂ à 3CO₂ + 4H₂O

Balancing Equations: Chemical equations must be balanced with respect to all atoms and the atoms must exist in real compounds.

1. You should leave elements that stand alone as elements until last when balancing chemical equations
2. Start by balancing an element that appears in only one reactant and product.
3. Once one element is balanced, proceed to balance another, and another, until all elements are balanced.
4. Balance chemical formulas by placing coefficients in front of them. Do not add subscripts, because this will change the formulas.

Rules for Balancing Equations:

1. Select the compound with the largest number of atoms of an element not including H or O or groups.
2. Balance this number of atoms with the corresponding atom on the other side of the equation with a coefficient (temporarily a fraction if necessary)...never change the compound.
3. Next balance any groups if they are present.
4. Now balance any H and O if they are present.

Patterns of Chemical Reactions:

1. Combination – combining two or more atoms or molecules to make one
2. Decomposition – taking one atom or molecule to make two
3. Displacement – replacement of one part with another
4. Exchange – swapping atoms or molecules

Examples of Balancing Equations:

Step 1. Insert 1 in front of the most complicated looking chemical compound.
1C₅H₁₂ + O₂ --> CO₂ + H₂O

Step 2. To balance C's, 5 must be inserted in front of CO₂.
1C₅H₁₂ + O₂ --> 5CO₂ + H₂O

Step 3. To balance H's, 6 must be inserted in front of H₂O .
1C₅H₁₂ + O₂ --> 5CO₂ + 6H₂O

Step 4. To balance O's, 8 must be inserted in front of O₂ .
1C₅H₁₂ + 8O₂ = 5CO₂ + 6H₂O

Erase 1 from the equation:

C₅H₁₂ + 8O₂ = 5CO₂ + 6H₂O

The equation is now in balance !
Note (balancing chemical equations): If any fractions should occur, simply multiply the chemical equation by a suitable number. This will be demonstrated in the next problem.


Problem 2 (Example balancing): Balance the chemical equation for combustion of ethane

Example balancing chemical equations

Step 1. Insert 1 in front of the most complicated looking chemical compound.
1C₂H₆ + O₂ à CO₂ + H₂O

Step 2. To balance C's, 2 must be inserted in front of CO₂.
1C₂H₆ + O₂ à  2CO₂ + H₂O

Step 3. To balance H's, 3 must be inserted in front of H₂O .
1C₂H₆ + O₂ à  2CO₂ + 3H₂O

Step 4. To balance O's, 7/2 must be inserted in front of O₂ .
1C₂H₆ + 7/2O₂ = 2CO₂ + 3H₂O

Step 5. Eliminate the fraction 7/2. This can be done by multiplying the chemical equation by 2.
2C₂H₆ + 7O₂ = 4CO₂ + 6H₂O

The equation is now in balance!

Most elements are monoatomic.