Question

2KClO3 = 3kCL +2o2 how many moles of KClO3 are needed to produce 4.5 moles of KCl?

Answer 1

Coefficients in the chemical equation show ratio of moles of the reactants and products. 
                                    2KCLO3 ----> 3KCl +2O2
by reaction                   2 mol               3 mol
from problem               x mol              4.5 mol

x=(2*4.5)/3 =9/3 =3 mol  of KClO3  are needed to form 4.5 mol KCl.