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MAKING
SENSE OF CHEMICAL EQUATIONS
Communication is an
important word in today's world. One way chemists can communicate
with information about a reaction is by writing a chemical equation.
Chemical equations form an international language. Chemists from
different countries can communicate with each other by equations. What does an equation
show?
It describes a real
event.
It tells you which
chemicals are reacting.
It uses a chemical
shorthand to describe a reaction. (symbols and formulae)
It tells you how
many particles are involved. (atoms, molecules and ions)
It tells you the
number of moles of each substance that react together.
It tells you the
number of moles of products formed. (These are the large numbers
in front of the formulae)
Many equations also
show whether a substance is a solid, liquid or gas or dissolved
in water. (state symbols, (s), (l), (g), or (aq).
WRITING
CHEMICAL EQUATIONS
- Write the equation
in words.
Make sure you include all the reactants and all the products.
- Now write the equation
in symbols, making sure you have used the correct formula for
each substance.
Remember that the
common gases are diatomic. ( they exist as pairs)
- Check the formula
of each compound and do not alter the small numbers
that are part of the formula.
If you cannot remember
the correct formula, you will have to work it out by the methods
shown in the Chemical Formula Worksheet.
- Balance the equation
so that the numbers of each atom on the left hand side are the
same as those on the right hand side.
You
can do this by a trial and error method!
- Check each atom
in turn and then change each side until the numbers are balanced.
Do this by putting
large numbers in front of the formulae.
The next section shows
two examples. Read through them and then try the problems for
yourself. Example 1:
"solid sodium
metal burns in chlorine gas to form solid sodium chloride."
Write the word equation:
sodium
+ chlorine à sodium chloride
Translate into symbols
and formulae:
| Na
+ Cl2 |
 |
NaCl
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Balance the equation:
Write down the numbers
of each atom on each side of the equation:
| LHS |
RHS |
| 1 Na |
1
Na |
| 2 Cl |
1
Cl |
There are more chlorine
atoms on the LHS, so increase the RHS by putting a large "2"
in front of the NaCl.
| LHS |
RHS |
| 1 Na |
2
Na |
| 2 Cl |
2
Cl |
There is only 1 sodium
atom on the LHS, so balance the equation completely by adding
a "2" in front of the Na.
The balanced equation
is thus:
| 2Na
+ Cl2 |
|
2NaCl |
It can also show
state symbols:
| 2Na(s)
+ Cl2(g) |
|
2NaCl(s) |
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