balancing+equations

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: CaCl 2 (aq) + Na 3 PO 4 (aq) --> NaCl (aq) + Ca 3 (PO 4 ) 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:

_CaCl 2 (aq) + _Na 3 PO 4 (aq) --> _NaCl (aq) + _Ca 3 (PO 4 ) 2 (s)

Now, separate the reactants and products, and list the ions or elements underneath:
 * _CaCl 2 (aq) + _Na 3 PO 4 (aq) --> || _NaCl (aq) + _Ca 3 (PO 4 ) 2 (s) ||
 * Ca || Ca ||
 * Cl || Cl ||
 * Na || Na ||
 * PO 4 || PO 4 ||

Note that PO 4 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:
 * _CaCl 2 (aq) + _Na 3 PO 4 (aq) --> || _NaCl (aq) + _Ca 3 (PO 4 ) 2 (s) ||
 * Ca 1 || Ca 3 ||
 * Cl 2 || Cl 1 ||
 * Na 3 || Na 1 ||
 * PO 4 1 || PO 4 2 ||

Start at the top (or anywhere, really) where the reactants side needs 3 Ca, but only has 1. Multiply CaCl 2 by 3 and re-count:


 * __3__CaCl 2 (aq) + _Na 3 PO 4 (aq) --> || _NaCl (aq) + _Ca 3 (PO 4 ) 2 (s) ||
 * Ca 3 || Ca 3 ||
 * Cl 6 || Cl 1 ||
 * Na 3 || Na 1 ||
 * PO 4 1 || PO 4 2 ||

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


 * __3__CaCl 2 (aq) + _Na 3 PO 4 (aq) --> || __6__NaCl (aq) + _Ca 3 (PO 4 ) 2 (s) ||
 * Ca 3 || Ca 3 ||
 * Cl 6 || Cl 6 ||
 * Na 3 || Na 6 ||
 * PO 4 1 || PO 4 2 ||

And now balance the Na's by doubling the Na 3 PO 4 :


 * __3__CaCl 2 (aq) + __2__Na 3 PO 4 (aq) --> || __6__NaCl (aq) + _Ca 3 (PO 4 ) 2 (s) ||
 * Ca 3 || Ca 3 ||
 * Cl 6 || Cl 6 ||
 * Na 6 || Na 6 ||
 * PO 4 2 || PO 4 2 ||

The final answer: 3 CaCl 2 (aq) + 2 Na 3 PO 4 (aq) --> 6 NaCl (aq) + Ca 3 (PO 4 ) 2 (s)

Here is a nice [|practice website] for balancing equations.

Here is an [|online chemical equation balancer].

Practice worksheet: