Stoichiometry Worksheet Page 5
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6Balancing Chemical Equations
There are three rules to follow when balancing chemical equations. They do not work every time, but they
do work most times and most people find them helpful.
If there is an element that is not bonded to any other atom or is diatomic, balance it last. For example in the
O C
equation: CO
+ H
H
O
+ O
, oxygen is diatomic. When balancing this equation, balance oxygen
2
2
6
12
6
2
last.
If you are balancing an equation with both hydrogen and oxygen and neither is a diatomic molecule,
balance hydrogen last and balance oxygen second to last. For example in the equation: CO
+ NH
-->
2
3
OC(NH
)
+ H
O, both hydrogen and oxygen are used and neither exist as a diatomic molecule. When
2
2
2
balancing this equation, balance hydrogen last and oxygen second to last.
If you come to the point where you have an odd number of a certain element on one side of the equation
and an even number of the same element on the opposite side on the equation, double the coefficient of the
formula with the odd number of the element. If the coefficient is 1, change it to 2.
Ultimately it is a trial and error process. Keep at it until it works. Here are 10 practice problems. The
answers are on the last page. Don’t cheat.
C + HCl
OC(NH
1. C
H
+ Cl
2. CO
+ NH
)
+ H
O
10
16
2
2
3
2
2
2
SiO
Al
3. Si
H
+ O
+ H
O
4. Al(OH)
+ H
SO
(SO
)
+ H
O
2
3
2
2
2
3
2
4
2
4
3
2
Fe
+ KOH K
5. Fe + O
O
6. Fe
(SO
)
SO
+ Fe(OH)
2
2
3
2
4
3
2
4
3
CO
+ HI H
7. C
H
O
+ O
+ H
O
8. H
SO
S + I
+ H
O
7
6
2
2
2
2
2
4
2
2
2
Stoichiometry (LO 3.3, 3.4)
I use the chart to the right to teach stoichiometry.
23
Particles
Particles
1 mole given
6.022 x 10
find
23
given
(ions*, atoms*
6.022 x 10
1 mole find
(ions*, atoms*
molecules &
molecules &
USE
formula units)
formula units)
BALANCED
EQUATION
Mass (g)
Moles
Moles
Mass (g)
1 mole given
MM find
moles of find substance
MM given
moles of given substance
1 mole find
1 mole given
22.4 L find
1 mole find
Volume(L)
Volume(L)
22.4 L given
of gas at STP
of gas at STP
START on THIS SIDE
FINISH on THIS SIDE
In a stoichiometry problem you always begin with a value of one of the units on the left and you always finish with a
value of one of the units on the right. In every stoichiometry problem you must make a mole relationship
comparison between substances being compared using their coefficients from the balanced chemical equation. This
concept is used extensively. If you need help, e-mail me or see me after school for help. Additional problems can be
found here: E-mail me for the answers.
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