Untitled - Kelly Walsh High School

Mass, Moles, and Equations 33
Careful!
Don’t Forget!
First, write an unbalanced equation, showing the reactants and products:
___Fe(s) ___ O 2(g) l ___ Fe 2O 3(s)
The blanks indicate where we will add coefficients. When balancing, you can
make no changes other then placing numbers in these blanks. Note that there
is one iron on the reactant side and two on the product side. To balance the iron
we need a coefficient of 2 in front of the Fe on the reactant (left) side:
2 Fe(s) ___ O 2(g) l ___ Fe 2O 3(s)
You can’t change the formulas of the reactants or products, just the coefficients.
The irons are balanced but there are 2 oxygens on the reactant side and 3 on
the product side. The oxygens enter the reaction in groups of two, O 2. We will
balance the oxygen atoms by placing a coefficient of 1.5 in front of the O 2 on
the left:
2 Fe(s) 1.5 O 2(g) l ___ Fe 2O 3(s)
That will give us 3 oxygens on both sides (1.5 2 3), but we must have coefficients
that are whole numbers. The easiest way to achieve this is to multiply
everything by 2:
2 [2 Fe(s) 1.5 O2(g) l 1 Fe2O3(s)] giving the balanced equation:
4 Fe(s) 3 O2(g) l 2 Fe2O3(s) If a particular coefficient is 1, we commonly omit it.
Make sure that all atoms balance and the coefficients are in the lowest whole
number ratio.