How to do you balance this chemical equation?

Question

C2H4Cl2 + O2 => CO2 +H2O +HCl


I know that I start like this...
C2H4Cl2 + O2 => 2CO2 + H2O + HCl

but how do you know where to go from there?
also how do you know when to double your results?
Please inform me on how to do these type of problems thank you

Answer 1

When balancing equations, I always give myself an order of the elements to try to balance first. This order almost always saves a lot of headache: Polyatomic ions, All except H and O, H, and finally O.

I will work this equation following that order:

C2H4Cl2 + O2 ~> CO2 +H2O + HCl

I see I need to double the carbons on the product side, like you saw as well.

C2H4Cl2 + O2 ~> 2 CO2 + H2O + HCl

Then I would double the chlorines on the product side to take care of them.

C2H4Cl2 + O2 ~> 2 CO2 + H2O + 2 HCl

Hydrogen is next, but I see they are already balanced. Finally, I see 2 Oxygens on the reactant side and 5 on my product side. 2 cannot divide into 5. So, this is the trick:

1) The odd number of oxygens on the product side becomes the coefficient for oxygen on the reactant side.

2) double the coefficients for all other compounds.

Your final balanced chemical equation is:

2 C2H4Cl2 + 5 O2 ~> 4 CO2 + 2 H2O + 4HCl