Limiting Reactants

Reactions stop when one reactant is used up

• When some magnesium carbonate is placed into a beaker of hydrochloric acid, you can tell a reaction is taking place because you see lots of bubbles of gas being given off
• After a while, the amount of fizzing slows down
  • The reaction stops when all reactants is used up
  • Reactants that’s used up in called limiting reactants
  • Amount of product formed is directly proportional to amount of limiting reactant
  • Because if you add more reactant there will be more reactant particles, meaning more product particles

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The amount of product depends on the limiting reactant

• You can calculate mass of product formed in a reaction by using the mass of the limiting reactant and the balanced reaction equation
  • Write out the balanced equation
  • Work out relative formula masses
  • Find out how many moles there are of the substance you know the mass of
  • Use balanced equation to work out how many moles there’ll be of the other substance
  • Use the number of moles to calculate the mass

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