February 26, 2014
Limiting Reactants
Why do chemical reactions stop?
February 26, 2014
Limiting reactant: limits the extent of the reaction.
• determines the amount of product
• the reactant that runs out first.
Excess reactant: Left-over reactants
February 26, 2014
Consider this reaction:
Practice 1:
N2 + H 2
NH3
1. Balance the equation.
2. If you have 3 moles of N2 and 3 mol of H2,
how many moles of NH3 can you make?
3. Which is the limiting reactant?
February 26, 2014
How to determine which reactant is the limiting
reactant:
If quantity (mass, moles) of both reactants are
given...
1. Determine the # of moles of product that can be
produced with the first reactant
2. Determine the # of moles of products that can be
produced with the second reactant
3. Compare: The reactant that results in less
product is the limiting reactant
February 26, 2014
Practice 2:
S8 + Cl2
S2Cl2
*Make sure to balance the equation
You have 100.0g of Cl2 and 200.0g of S8.
Which reactant is the limiting reactant?
February 26, 2014
Practice 2:
S8 + Cl2
S2Cl2
*Make sure to balance the equation
You have 100.0g of Cl2 and 200.0g of S8.
Which reactant is the limiting reactant?
*How many grams of S2Cl2 can be produced?
February 26, 2014
How do you figure out how much reactant you have left
over?
1. Figure out how much reactant was used
2. Subtract from starting amount.
February 26, 2014
Practice 3:
S8 + Cl2
S2Cl2
*Make sure to balance the equation
You have 100.0g of Cl2 and 200.0g of S8.
**How many grams of the excess reactant is left?
February 26, 2014
Theoretical yield: maximum amount of product that
can be produced from a given amount of reactant.
Actual yield: The amount of product actually
produced
Percent yield: Tells you efficiency of reaction.
Percent yield =
actual yield
theoretical yield
x 100
February 26, 2014
Practice 4:
Excess potassium chromate and 0.455g silver nitrate
are mixed to form silver chromate.
What is the theoretical yield of silver chromate?
If 0.455g of silver chromate is obtained, what is the
percent yield?