Chemistry Reference
In-Depth Information
Zn + H
2
SO
4
ZnSO
4
+ H
2
Elements
{
# of atoms
{
12141214
Zn
H
S
O
Zn
H
S
O
Already balanced!
Did we get the same answers? Do you notice that this chemical equa-
tion doesn't show any coefficients? Sometimes, a chemical equation is bal-
anced when all of the substances have a coefficient of “1.” When the
coefficient for a substance is “1,” we don't write it, and the “1” is under-
stood. If you are ever asked to balance a chemical reaction that is already
balanced, with no coefficients written in, simply write, “Already balanced,”
and your instructor will know that you did your atomic tally correctly.
Let's try another example. Can you do the atomic tally for the next
example?
Example 2
Do an atomic tally for the following equation and determine if it is
balanced.
Mg + O
2
MgO
Remember: Do the tally on your own before checking your answer.
Mg + O
2
MgO
Elements
{
# of atoms
{
Mg
O
Mg
O
1211
Not balanced!
Can you see why I said that this equation is not balanced? On the reac-
tant side, two atoms of oxygen appear, yet on the product side, we only see
one atom of oxygen. What are we allowed to do in this situation, if we want
to balance the equation? Follow the rule that follows!
Never, never, never change (add, subtract, or alter) a subscript in an
attempt to balance an equation!!!!
A sure sign of a beginner is that he or she will simply add a subscript in
an attempt to balance an equation. For example, if a beginner wanted to
balance the equation from Example 2, he or she might write:
Mg + O
2
MgO
2
Can you see why this is not the correct procedure for balancing an equa-
tion? By adding a subscript of “2” to the MgO, we have changed the way
