Limiting Reactants

Unit 8: Stoichiometry

• 4 Legs + 1 Top 1 TableThis is a table…

• ONE table• Why?–You run out of table legs!

How many tables can you build with six table legs?

• TWO tables• What do

you run out of first?–Table Tops

• What do you have extra of?–Table Legs

How many tables can you build with 2 table tops and 9 legs?

• In a chemical reaction, one reactant may run out before another…–You have too many of one thing and not enough of the other

• The reactant that is not left over (not in excess) is the limiting reactant

What are limiting reactants?

• The limiting reactant is the reactant that is not present in excess• The limiting reactant will be

used up first • The limiting reactant

therefore limits the amount of product that can be formed by the reaction

What are limiting reactants?

• LR “limits” or determines the number of reactions that can take place• When the LR runs out the

reaction stops!• LR determines how much

product that can be made• LR determines how much of the

other reactant is left over

What are limiting reactants?

• The excess reactant (XS) is the reactant that is left over, unused after the LR runs out and the reaction stops

What is an excess reactant?

• How many batches of cookies can be made with the ingredients in the pantry?

Practice

• Each ingredient has enough to make how many batches of cookies? Least # of batches = LR

Practice

You are in lab and you are making water from the reaction of hydrogen gas and oxygen gas. You have 6 moles of hydrogen and 4 moles of oxygen. What are the limiting and excess reactants?

Practice

2 H2 + 1 O2 → 2 H2OHow many reactions can be made with 6 mol Hydrogen?

How many reactions can be made with 4 mol Oxygen?

LR?

Practice