Take 1 ball of one colour. This represents a molecule of
. Take two balls of another colour and stick them together. This represents a molecule of
. Place these molecules on your left. Now take two balls of one colour and three balls of another colour to form a molecule of
. Place these molecules on your right. On a piece of paper draw coloured circles to represent the balls. Draw a line down the center of the paper to represent the molecules on the left and on the right.
Count the number of balls on the left and the number on the right. Do you have the same number of each colour on both sides? If not the equation is not balanced. How many balls will you have to add to each side to make the number of balls the same? How would you add these balls?
You should find that you need 4 balls of one colour for
and 3 pairs of balls of another colour (i.e. 6 balls in total) for
on the left side. On the right side you should find that you need 2 clusters of balls for
.
We say that the balanced equation is:
Repeat this process for the following reactions:
Steps to balance a chemical equation
When balancing a chemical equation, there are a number of steps that need to be followed.
STEP 1: Identify the reactants and the products in the reaction and write their chemical formulae.
STEP 2: Write the equation by putting the reactants on the left of the arrow and the products on the right.
STEP 3: Count the number of atoms of each element in the reactants and the number of atoms of each element in the products.
STEP 4: If the equation is not balanced, change the coefficients of the molecules until the number of atoms of each element on either side of the equation balance.
STEP 5: Check that the atoms are in fact balanced.
STEP 6 (we will look at this a little later): Add any extra details to the equation e.g. phase.
Balance the following equation:
Reactants:
;
and
Products:
;
and
The equation is not balanced since there are 2 chlorine atoms in the product and only 1 in the reactants. If we add a coefficient of 2 to the
to increase the number of
and
atoms in the reactants, the equation will look like this:
If we count the atoms on each side of the equation, we find the following:
Reactants:
;
and
Products:
;
and
The equation is balanced. The final equation is:
Balance the following equation:
Reactants:
;
and
Products:
;
and
If we add a coefficient of 2 to
, then the number of hydrogen atoms in the reactants will be 4, which is the same as for the reactants. The equation will be:
Reactants:
;
and
Products:
;
and
You will see that, although the number of
hydrogen atoms now balances, there are more oxygen atoms in the products. You now need to repeat the previous step. If we put a coefficient of 2 in front of
, then we will increase the number of oxygen atoms in the reactants by 2. The new equation is:
When we check the number of atoms again, we find that the number of atoms of each element in the reactants is the same as the number in the products. The equation is now balanced.
Nitrogen gas reacts with hydrogen gas to form ammonia. Write a balanced chemical equation for this reaction.
The reactants are nitrogen (
) and hydrogen (
) and the product is ammonia (
).
The equation is as follows:
Reactants:
and
Products:
and
In order to balance the number of nitrogen atoms, we could rewrite the equation as:
In the above equation, the nitrogen atoms now balance, but the hydrogen atoms don't (there are 2 hydrogen atoms in the reactants and 6 in the product). If we put a coefficient of 3 in front of the hydrogen (
), then the hydrogen atoms and the nitrogen atoms balance. The final equation is:
In our bodies, sugar (
) reacts with the oxygen we breathe in to produce carbon dioxide, water and energy. Write the balanced equation for this reaction.
Reactants: sugar (
) and oxygen (
)
Products: carbon dioxide (
) and water (
)
Reactants:
;
and
Products:
;
and
It is easier to start with carbon as it only appears once on each side. If we add a 6 in front of
, the equation looks like this:
Reactants:
;
and
Products:
;
and
Let's try to get the number of hydrogens the same this time.
Reactants:
;
and
Products:
;
and
Reactants:
;
and
Products:
;
and
This simulation allows you to practice balancing simple equations.
run demo
Balancing simple chemical equations
Balance the following equations:
Hydrogen fuel cells are extremely important in the development of alternative energy sources. Many of these cells work by reacting hydrogen and oxygen gases together to form water, a reaction which also produces electricity. Balance the following equation:
The synthesis of ammonia (
), made famous by the German chemist Fritz Haber in the early 20th century, is one of the most important reactions in the chemical industry. Balance the following equation used to produce ammonia:
Barium chloride reacts with sulphuric acid to produce barium sulphate and hydrochloric acid.
Ethane (
) reacts with oxygen to form carbon dioxide and steam.
Ammonium carbonate is often used as a smelling salt. Balance the following reaction for the decomposition of ammonium carbonate:
