Limiting Reactantsand

Percent Yield

Definitions

• The Limiting Reactant is the reactant that limits the amounts of the other reactants that can combine and the amount of product that can form in a chemical reaction. Reactant run out of first.

• The excess reactant is the substance that is not used up in a reaction. Reactant we have left overs.

1engine + 4 tires → 1 car

• If you have two engines and seven tires which is your limiting reactant and which is in excess?

2 engines

1 engine

4 tires= 8 tires

Practice problem#1

• SiO2 + 4HF → SiF4 + 2H2O

• If 2.0 moles of HF are exposed to 4.5 moles of SiO2, which is the limiting factor?

2 mol HF

4 moles HF

1 mole SiO2 = 0.5 moles SiO2

Practice problems

2. N2H4 + 2H2O2→ N2 + 4 H2O

a) Which is the limiting reactant in this reaction when 112g of N2H4 is mixed with 125g of H2O2?

b) How much of each product could be produced, in grams?

Practice problems

• Pg.368 #21

Percent Yield

• The theoretical yield is the maximum amount of product that can be produced from a given amount of reactant. (The result of a mass-mass problem)

• The actual yield is the actual amount of a product obtained from a reaction.

When 36.8 g of C6H6 react with excess Cl2, the actual yield of C6H5Cl is 38.8g. What is

the percent yield of C6H5Cl?

• C6H6 + Cl2 → C6H5Cl + HCl

• Do a mass-mass problem to determine your theoretical yield.

• Divide your actual yield by your theoretical yield and convert to percent.

theoretical yield

actual yield=

38.8g

53.0g= .732 x100 = 73.2%