So to balance an equation, you need to get the same amount of each type of element on either side of the --> . So you pretty much are given the subscripts in the equations and you need to add coefficients (just normal numbers) in front of any formula that needs it, keeping anything balance.
[tex]KCl_{3} + O_{2} -\ \textgreater \ KCl_{3} [/tex]
turns into
[tex]2KCl_{3}+ 3O_{2} -> 2KCl_{3} [/tex]
These coefficient numbers are the molar ratios, so 2 moles of KCl3 for every 3 moles of O2 so 1. 3:2
Then you can use these ratios of find out how many moles of one thing are needed if you are given the amount of another.
[tex] \frac{moles of element 1}{cofficient 1} = \frac{moles of element 2}{cofficient 2} [/tex]
and use cross multiplication to solve for whatever you don't know
