1. Balancing Chemical Equations
Explaining the Concepts…

2. Let’s look at the reaction between Hydrogen gas and Oxygen gas to form Water.

3. We see in one container Hydrogen gas …which is made up of molecules having two atoms each.
We call this a diatomic molecule.
In the second container we have Oxygen gas... which is also a diatomic molecule.

4. These two gasses react with each other… to form water.
In this reaction Hydrogen and Oxygen are called reactants because they react with each other.
Water is called a product in this reaction because it is the substance being formed.

5. Oxygen can be represented in different ways.
This is what we see
This is how we represent it on a submicroscopic level
This is how we write it in symbolic form
Hydrogen can also be represented in these forms

6. And in the same way, Water…

7. Notice that in the symbolic representation of Oxygen the subscript 2 means that 2 oxygen atoms bond together to form each oxygen molecule.
This is similar for Hydrogen because it is also a diatomic molecule.
The water formula is H2O which could also be written as H2O1. These subscripts refer to the fact that 2 Hydrogen atoms are bonded to 1 Oxygen atom within each water molecule.

8. Two water molecules are shown in this picture
Two water molecules are shown in this picture. This can be represented as 2H2O. The coefficient 2 refers to the fact that there are 2 water molecules present.

9. To form these water molecules two oxygen atoms needed to react.
These came from 1 oxygen molecule which can be represented as 1 O2
but we normally write this as simply O2.
To form these 2 water molecules, 4 hydrogen atoms were needed. These came from 2 hydrogen molecules which can be represented as 2 H2.
The coefficient 2 refers to the fact that there were 2 hydrogen molecules reacting.

10. =
The complete reaction can be represented by a chemical equation as shown here.
The coefficients in this equation refer to the ratio in which the substances react.
Notice also that this equation is balanced.
This means that the mass of the reactants equals the mass of the product. This is because matter was not created or destroyed during this reaction; the atoms simply rearranged.
We describe this as the Law of Conservation of Matter.

11. Law of Conservation of Matter
Matter cannot be
created or destroyed
The Law of Conservation of Matter states that matter cannot be created or destroyed.

12. Notice also that a water molecule always consists of 2 Hydrogen atoms bonded to 1 Oxygen atom
This is because of the arrangement of electrons in the Hydrogen and Oxygen atoms

13. Law of Constant Proportions
In any particular chemical compound, all samples of that compound will be made up of the same elements in the same proportion or ratio.
 This is described by the Law of Constant Proportions…
The Law of Constant Proportions states that in any particular chemical compound, all samples of that compound will be made up of the same elements in the same proportion or ratio.