Reactants, Products and Leftovers – Interactive PhET Simulation

Explore reactants, products and leftovers

Chemical equations tell us the proportions in which substances react, but in real mixtures the reactants are not always present in exactly the required amounts.

This interactive PhET simulation allows you to explore stoichiometric ratios, limiting reactants and excess reactants by changing the quantities of substances taking part in a reaction and observing how much product can be formed.

Make your prediction before running each reaction. Decide which reactant will run out first, how much product should form and whether any reactant will be left over. Then use the simulation to test your reasoning.

Reactants, Products and Leftovers is provided by PhET Interactive Simulations, University of Colorado Boulder, and is used under the CC BY-NC 4.0 licence.

Try these challenges

1. Read the reaction ratio
Before adding any reactants, examine the balanced equation. What does it tell you about the numbers of particles required to react completely?

2. Make a perfect mixture
Choose quantities of reactants that react completely, leaving no reactant left over. How does the balanced equation help you choose the correct amounts?

3. Create an excess reactant
Add more of one reactant than is required. Predict how much product will form and how much reactant will remain when the reaction is complete.

4. Identify the limiting reactant
Choose quantities that are not in the correct stoichiometric ratio. Before running the reaction, decide which reactant will be used up completely. This is the limiting reactant.

5. Change the limiting reactant
Without changing the reaction itself, alter the quantities so that the other reactant becomes limiting. Explain what you changed and why the limiting reactant changed.

6. Maximise the product
Keep the amount of one reactant fixed and gradually add more of the other. At what point does adding more cease to increase the amount of product? Explain why.

7. Connect particles to moles
The simulation uses numbers of particles, but the same ratios apply to amounts measured in moles. If the equation requires two particles of A for every one particle of B, what mole ratio would be required?

The key question

Keep asking:

Which reactant determines the maximum amount of product that can be formed?

Finding the limiting reactant is the key to solving many quantitative chemistry problems.

 
 
 
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