Limiting Reactants (OCR GCSE Chemistry A, Combined (Gateway Science Suite)): Revision Notes

In a chemical reaction, the limiting reactant is the substance that gets used up first, limiting the amount of product that can be formed. Once this reactant is gone, the reaction stops, even if other reactants are still available.

Worked Example:

• Let's say 7.95 g of copper oxide $(CuO)$ reacts with 7.2 g of carbon $(C)$ to produce copper $(Cu)$and carbon dioxide $(CO₂$):

1. Calculate the moles:

• Moles of CuO:

• Moles of C:

2. Determine the limiting reactant:

• The balanced equation shows $CuO$ and $C$ react in a 2:1 ratio. To react with 0.1 moles of $CuO$, you only need 0.05 moles of carbon. Since we have much more carbon, CuO is the limiting reactant.

3. Calculate the mass of products:

• Using the mole ratio from the balanced equation, 0.1 moles of $CuO$ will produce 0.1 moles of $Cu$ and 0.05 moles of $CO₂$.
• Mass of Cu:

• Mass of CO₂: