What is meant by the limiting reactant in a chemical reaction?

It is the reactant that is completely used up, and it limits the amount of product that can be made.

Two reactants are mixed and one is in excess. Which one would you weigh out carefully if you wanted to control the mass of product made?

The limiting reactant, because the amount of product is fixed by the amount of that reactant.

Explain why adding more of the excess reactant to a finished reaction makes no more product.

The limiting reactant has already been completely used up, so there is nothing left for the extra reactant to react with.

AQA GCSE Combined Science Chemistry 8464

Atomic Structure and the Periodic Table

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Organic Chemistry

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Quantitative Chemistry

Topic overview Conservation of mass and balanced chemical equations Relative formula mass and concentration of solutions Mass changes when a gas is involved, and measurement uncertainty Moles Amounts of substances in equations, and balancing using moles Limiting reactants

The Rate and Extent of Chemical Change

Topic overview Measuring the mean rate of a reaction Rate from graphs, and the gradient of a tangent Factors which affect the rates of chemical reactions Collision theory and activation energy Catalysts Reversible reactions and dynamic equilibrium The effect of changing conditions on equilibrium The effect of changing concentration The effect of temperature changes on equilibrium The effect of pressure changes on equilibrium

Using Resources

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Quantitative Chemistry

Limiting reactants

3 things to know
Chemistry Paper 1

Overview

What the limiting reactant is, why one reactant is used in excess and what happens to it, which reactant fixes the mass of product, and worked examples with magnesium, oxygen, acid and ammonia.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Why is one of the two reactants often used in excess?

Key term

What happens to the reactant that is present in excess?

Key term

Which of two reactants decides the maximum amount of product that can form?

Questions from this subtopic

Each one with the model answer underneath.

1
What is meant by the limiting reactant in a chemical reaction?
Model answer
It is the reactant that is completely used up, and it limits the amount of product that can be made.
2
Why is one of the two reactants often used in excess?
Model answer
To make sure that all of the other reactant is used up in the reaction.
3
What happens to the reactant that is present in excess?
Model answer
Some of it is left over unreacted at the end of the reaction.
4
Which of two reactants decides the maximum amount of product that can form?
Model answer
The limiting reactant, the one that runs out first.
5
Two reactants are mixed and one is in excess. Which one would you weigh out carefully if you wanted to control the mass of product made?
Model answer
The limiting reactant, because the amount of product is fixed by the amount of that reactant.
6
Explain why adding more of the excess reactant to a finished reaction makes no more product.
Model answer
The limiting reactant has already been completely used up, so there is nothing left for the extra reactant to react with.

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Atomic Structure and the Periodic Table

Bonding, Structure, and the Properties of Matter

Chemical Analysis

Chemical Changes

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