Balancing reactions

We'll start balancing reactions assuming that you already have the formulas written correctly. This is very important since it is often impossible to balance a reaction in which the formulas are written incorrectly, and even if you get it balanced, it is still wrong. If you aren’t sure about writing formulas, you can go back to nomenclature.

Balancing reactions is largely a process of trial and error. There is, unfortunately, no simple process that always works. There are a few common situations and types that we will try to show here, but in the end, you will have to do some guess and check work.

Let's start with a simple example:


Ba(NO3)2 + Na2SO4 → NaNO3 + BaSO4

If we do a quick count we discover that there are the following atoms on each side of the equation:

Left side

Right side

Ba = 1

Ba = 1

N = 2

N = 1

Na = 2

Na = 1

O = 10 (6 from the 2 nitrates and 4 from sulfate)

O = 7 (3 from nitrate and 4 from sulfate)

S = 1

S = 1

It is also perfectly okay (and often easier) to count polyatomic ions as complete units. Of course this only works if the ion is identical on both sides. In other words, it will work here, but it wouldn't work in an equation that had sulfate (SO4) on one side and sulfite (SO3) on the other.

If we count by ions, we would have:

Ba(NO3)2 + Na2SO4 → NaNO3 + BaSO4

Left side

Right side

Ba = 1

Ba = 1

NO3 = 2

NO3 = 1

Na = 2

Na = 1

SO4 = 1

SO4 = 1

The reaction is not balanced because there are different numbers of nitrates and sodium atoms. So what can we do?

The answer is here.

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