To balance a chemical equation, follow these steps for the best results:
  1. Separate the reactants and products by drawing a line down the middle of the equation.
  2. List each type of element on each side; keep the order the same.
  3. Count up the number of atoms for each element and record them in the list.
  4. Look for an element that is easy to match through multiplying with a coefficient; place the coefficient in front of the compound.
  5. Modify and check the coefficients until the number of elements on each side match up.


Practice Problem:

Balance the equation: CaCl2 (aq) + Na3PO4 (aq) --> NaCl (aq) + Ca3(PO4)2 (s)

First, you can only modify the number of atoms by placing numbers in front of each compound. To remember this, re-write the equation with blank spaces, like this:

_CaCl2 (aq) + _Na3PO4 (aq) --> _NaCl (aq) + _Ca3(PO4)2 (s)

Now, separate the reactants and products, and list the ions or elements underneath:
_CaCl2 (aq) + _Na3PO4 (aq) -->
_NaCl (aq) + _Ca3(PO4)2 (s)
Ca
Ca
Cl
Cl
Na
Na
PO4
PO4

Note that PO4 can be kept as one polyatomic ion; this can be done as long as its formula is the same on both sides of the equation.

Count the number of ions for each item:
_CaCl2 (aq) + _Na3PO4 (aq) -->
_NaCl (aq) + _Ca3(PO4)2 (s)
Ca 1
Ca 3
Cl 2
Cl 1
Na 3
Na 1
PO4 1
PO4 2

Start at the top (or anywhere, really) where the reactants side needs 3 Ca, but only has 1. Multiply CaCl2 by 3 and re-count:

3CaCl2 (aq) + _Na3PO4 (aq) -->
_NaCl (aq) + _Ca3(PO4)2 (s)
Ca 3
Ca 3
Cl 6
Cl 1
Na 3
Na 1
PO4 1
PO4 2

Next is Cl: multiply NaCl by 6 to balance the Cl's:

3CaCl2 (aq) + _Na3PO4 (aq) -->
6NaCl (aq) + _Ca3(PO4)2 (s)
Ca 3
Ca 3
Cl 6
Cl 6
Na 3
Na 6
PO4 1
PO4 2

And now balance the Na's by doubling the Na3PO4:

3CaCl2 (aq) + 2Na3PO4 (aq) -->
6NaCl (aq) + _Ca3(PO4)2 (s)
Ca 3
Ca 3
Cl 6
Cl 6
Na 6
Na 6
PO4 2
PO4 2

The final answer: 3 CaCl2 (aq) + 2 Na3PO4 (aq) --> 6 NaCl (aq) + Ca3(PO4)2 (s)


Here is a nice practice website for balancing equations.

Here is an online chemical equation balancer.

Practice worksheet: