Limiting reactant
The reactant that is used up first, which stops the reaction and limits how much product forms. The other reactant is in excess.
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Analogy
If you have 10 slices of bread and 3 slices of cheese, you can only make 3 cheese sandwiches. The cheese is limiting.
In practice
Chemists add extra of a cheap reactant to make sure the expensive one is all used up.
Practice
Flashcards
- What is a limiting reactant?The reactant used up first, which stops the reaction.
Interview questions
- Explain what a limiting reactant is and why it matters to a manufacturer.
- It is used up first
- It limits the amount of product
- The other reactant is in excess
- Using excess of the cheaper reactant makes sure the costly one is used completely
Questions people ask
How do you find the limiting reactant?
Convert each reactant to moles. Divide by its coefficient in the balanced equation. The smaller result is the limiting reactant. For 2H2 + O2 -> 2H2O with 4 mol of hydrogen and 3 mol of oxygen, hydrogen gives 2 and oxygen gives 3, so hydrogen limits.
What does excess mean?
A reactant in excess is present in a larger amount than needed. Some will be left over when the reaction ends. In a reaction between magnesium and acid, if the magnesium is in excess, bubbling stops when the acid is used up and magnesium remains in the flask.