gcsescience.com 19 gcsescience.com

How to Balance Chemical Equations - Example 1.

When we are balancing
chemical equations we first

need to know
what the symbols and numbers
mean.

Click
here if you are not sure.

Example 1 is the reaction between potassium and chlorine.

(1)
K + Cl_{2}
KCl

On the left side of the arrow, there is 1K and 2Cl.

The two chlorines in Cl_{2}
cannot be changed,

since Cl_{2} is the formula of chlorine.

On the right side of the arrow, there is 1K and 1Cl.

The reaction is not
balanced

because atoms are not
gained or lost
in a chemical reaction.

The right side needs an extra
chlorine.

A big
number in front of the
symbol

changes the number of
elements in the formula
that follows it.

2K means two potassium ions. 2Cl_{2} means
four chlorine atoms.

2KCl
means two potassium ions with
two chlorine ions.

To get an extra chlorine on the
right side, we can put a 2 before KCl.

The equation becomes

(2) K + Cl_{2}
2KCl

Now the equation is balanced for chlorine, 2 on each
side.

But the equation has now become unbalanced for potassium.

There is 1 on the left and 2 on the right.

To get an extra potassium on the left, we can put a 2 before
K.

(3) 2K + Cl_{2}
2KCl

The equation is now balanced.

On the left there are 2 potassiums and
2 chlorines.

On the right there are 2 potassiums
and 2 chlorines.

Showing the three steps together, we have

(1)
K + Cl_{2}
KCl unbalanced for chlorine.

(2)
K + Cl_{2}
2KCl unbalanced for potassium.

(3) 2K + Cl_{2}
2KCl
Balanced!

See example 2. The reaction of lithium with oxygen.

Links
Revision Quizzes
Revision Questions

gcsescience.com The Periodic Table Index Balancing Equations Quiz gcsescience.com

**Home**
**GCSE Chemistry**
**GCSE Physics**

Copyright © 2015 gcsescience.com. All Rights Reserved.