Potassium chlorate solid decomposes to form solid potassium chloride and oxygen gas.


Balancing The Chemical Equation For The Decomposition of Potassium Chlorate

The purpose of balancing a chemical equation is to find the relative quantities of the molecules and atom types in the equation.  When the equation is balanced there will be the same number of each atom type on opposite sides of the equation. Consider the unbalanced equation for decomposition of potassium chlorate.

                                     KClO(s)  KCl(s)  + O₂(g)

                                     K=0                   K=0

                                    Cl=0                   Cl=0

                                     O=0                   O=0

The reactant side containing potassium chlorate and the product side containing potassium chloride solid and oxygen gas do not have equal numbers of each atom type.  There appears to be one potassium atom, one chlorine atom and three oxygen atoms on the left of the arrow and one potassium atom, one chlorine atom and two oxygen atoms on the right.  This makes the potassium and chlorine appear to be balanced and the oxygen to be unbalanced.  All of the atom types must be equal before the equation is balanced. To make the number of each type of atom on opposite sides of the arrow equal, the coefficients must be adjusted until the equation is balanced.  Compare the following results. 

                                     2KClO(s)  2KCl(s)  + 3O₂(g)

                                     K=2                   K=2

                                    Cl=2                   Cl=2

                                     O=6                   O=6

The coefficient 2 in front of the KClO₃(s) results in 2 atoms of potassium, 2 atoms of chlorine and 6 atoms of oxygen on the left side of the arrow.  The coefficient 2 in front of the KCl(s) results in 2 atoms of potassium and 2 atoms of chlorine on the right side of the arrow.  The coefficient 3 in front of the O₂(g) results in 6 atoms of oxygen on the right side of the arrow. The equation is balanced.  The ratio of coefficients 2:2:3 balances the reaction. The ratio of coefficients 4:4:6, 6:6:9 and 8:8:12, also, balance the reaction; however, the lowest ratio of coefficients 2:2:3 is the accepted answer.


© Pat Thayer 2014-2016