Using moles to balance equations (HT only)
Lajoy Tucker
Teacher
Contents
Definition
A balanced symbol equation shows the same number of each type of atom on both sides of a chemical reaction.
Balancing ensures the law of conservation of mass is obeyed – no atoms are lost or made during a reaction.
Balancing can be done using moles, since the number of moles is directly related to the number of particles involved.
The concept of the mole allows us to interpret chemical equations quantitatively.
For example:
This means:
2 moles of hydrogen react with 1 mole of oxygen
to produce 2 moles of water
The ratios of moles in equations show the proportions of substances reacting and being produced.
From Mass to Moles
1. Compare the number of moles of each substance.
2. Simplify the ratio to the smallest whole numbers to balance the equation.
0.015 mol of iron reacts with 0.01 mol of oxygen gas. Determine the formula of iron oxide made and give a balanced symbol equation for the reaction.
Question:
2.00 hydrogen and 16.0g oxygen react. Which balanced equation fits the data?
Two possible balanced equations:
Formation of water:
Formation of hydrogen peroxide:
Hydrogen Oxygen
Answer:
Step 1 – Convert Masses to Moles
Hydrogen
Oxygen
Step 2 – Find the Mole Ratio
Divide both numbers by the smaller value 0.500:
So, the experimental mole ratio is
Conclusion - The data support Equation 1 (formation of water):