Equations
Chemistry: AQA GCSE Higher, topic 3.1.7
Balancing Chemical Equations
Chemical equations must be balanced to make sure that there are the same number of atoms of each element before and after a reaction. The reaction of hydrogen with oxygen to make water will be used as an example of how to do this:
Unbalanced equation
- The unbalanced symbol equation for this reaction is:
- H2 + O2 → H2O
- The equation is unbalanced because there are 2 atoms of oxygen on the left hand side of the equation, but only 1 on the right hand side.
Still unbalanced equation
- We can increase the number of oxygen atoms on the right hand side by adding an H2O molecule:
- H2 + O2 → 2H2O
- However, the equation is still unbalanced as there are now more hydrogen atoms on the right hand side than on the left hand side.
Balanced equation
- The final step is to add an H2 molecule to the left hand side:
- 2H2 + O2 → 2H2O
- Our equation is now balanced.
Test yourself on Equations
H2 + O2 → 2H2O
Why is this equation unbalanced?Select the true statement in each pair.
How many nitrogen atoms are on the right hand side of the equation N2 + 3H2 → 2NH3?
What is the total number of reactant molecules shown on the left hand side of the equation N2 + 3H2 → 2NH3?
If every coefficient in the equation 2H2 + O2 → 2H2O is doubled to give 4H2 + 2O2 → 4H2O, is the new equation still balanced?