How to balance chemical equations with fractions?

You have to use a whole integer before the formula, so you don't use a fraction.  So you don't balance an equation with 1/2 etc., you double it.

Since C6H12O has an odd number of oxygens, you have to start with 2 C6H12O and go from there.

Usually when you are balancing a combustion reaction you want to balance carbons first, hydrogen second, and oxygen last.

_ C6H12O + _ O2 = 6CO2 + _ H2O  ->balances carbon

_ C6H12O + _ O2 = 6CO2 + 6H2O   ->balances hydrogen

Now you are left with 18 oxygen on the product side and need to balance the oxygen. This is where some professors will throw in the 'fraction method'

In order to balance the oxygen without disrupting the C6H12O that we already balanced most of, we use a fractional amount for the coefficient in front of O2. If we could put 17/2 (8.5) in front of O2 it would be balanced, right? So lets do that:

_ C6H12O + 17/ 2 O2 = 6CO2 + 6H2O
This equation is balanced, but now we would like to get rid of the fraction, so we multiply the entire reaction by 2:


2 C6H12O + 17 O2 = 12 CO2 + 12 H2O

And there is your balanced chemical equation. I believe the trick is that if your carbon compound has an even number of carbons, you will use this method.

Hope that clears things up a bit.