Balancing Equations
The best way to explain balancing equations is to show you
Worded Equation
Aluminium + Oxygen → Aluminium Oxide
Chemical Equation
Al + O2 → Al2O3
Balanced chemical Equation
4Al + 3O2 → 2Al2O3
Lets use the equation above, and explain how we came to this balanced equation.
The first thing, is to understand what a balanced equation is. This means both sides of the equation must have the same number of atoms of each element.
We can see from our initial equation that both sides aren’t balanced.
Al + O2 → Al2O3
Where did we get the extra Oxygen and Aluminium molecule?
What we have to do know is try and get the same number of atoms of each element on both sides of the equation.
First thing is, lets compare how many atoms of each element there are on each side.
There is 1 Aluminium (Al) and 2 Oxygen atoms (O2) on one side, and 2 aluminium and 3 oxygen (Al2O3) on the other side
Lets fix one element at a time.
At the end of the reaction, we end up with 2 Aluminium atoms.
To fix this, lets add an extra one to the start of our equation. (Click Add)
Now we get 2Al on one side. We’ve balanced the Aluminium, but our Oxygen atoms are still unbalanced.
When dealing with chemicals, we can’t add half a molecule. We only work in wholes.
The equation:
2Al +1.5O2 → Al2O3
Is NOT correct.
What we can do however is a bit of maths.
This is your current formula:
2Al +1.5O2 → Al2O3
We can’t leave it as a ½ so to get rid of that, we can multiply both sides by 2.
2(2Al +1.5O2) →2(Al2O3)
This makes:
4Al + 3O2 → 2Al2O3
Questions
1. What is the chemical formula for Potassium hydroxide
2. What is the chemical formula for hydrogen
3. Explain what a Diatomic molecule is and give 2 examples
4. What is the chemical formula for lithium chloride
5. What is the ‘law of conservation of mass’
6. Write out the worded equation, then write out the chemical symbols for each chemical. Finally re-
a. Magnesium + Hydrochloric acid → Magnesium Chloride + hydrogen
b. Sodium + water → Sodium hydroxide + hydrogen
c. Chromium (III) oxide + Magnesium → Chromium + Magnesium Oxide
7. Balance the following equations
a. Sr + O2 → SrO
b. H2 + O2 → H2O
c. Al + O2 → Al2O3
d. C3H6 + O2 → CO2 + H2O
e. As4S6 + O2 → As4O6 + SO2
f. CH4 + O2 →CO2 + H2O
g. CH4 + Cl2 →CCl4 + HCl
h. Mg + O2 → MgO
i. CaCl2 + Na3PO4 → Ca3(PO4)2 + NaCl
j. H2SO4 + Pb(OH)4 → Pb(SO4)2 + H2O
Before we start it’s important to remember what Diatomic molecules are. Diatomic molecules are made up of two atoms joined together. Hydrogen gas (H2), for example, is a diatomic molecule because it is made from two hydrogen atoms joined together, as is the oxygen molecule (O2) which contains two oxygen atoms.
Lets start simple
Worded equation
Hydrogen + Oxygen → Water
Chemical equation
H2 + O2 → H2O
The first thing we notice is that there are more oxygen molecules on one side.
This means the equation is un-
Our hydrogen molecules are balanced but our oxygen molecules are not.
Let add another H2O molecule to the other side.
The problem is, now we have too many hydrogen atoms on one side.
Now, lets balance the hydrogen. Lets add another 2 hydrogen molecules to one side.
Now we have a balanced equation. There is equal amounts of each element on each side
Balanced Equation
2H2 + O2 → 2H2O