Math in Chemistry

Limiting Reactants

and Yield

Limiting Reactants

Available IngredientsAvailable Ingredients 4 slices of bread 1 jar of peanut butter 1/2 jar of jelly

Limiting ReactantLimiting Reactant bread

Excess ReactantsExcess Reactants peanut butter and jelly

A. Limiting Reactants Limiting ReactantLimiting Reactant

used up in a reaction determines the amount of product

Excess ReactantExcess Reactant added to ensure that the other reactant is

completely used up cheaper & easier to recycle

Limiting Reactants

1. Write a balanced equation.

2. For each reactant, calculate the amount of

product formed.

3. Smaller answer indicates: limiting reactant amount of product

Limiting Reactants

79.1 g of zinc react with 0.90 L of HCl. Identify the limiting and excess reactants. How many liters of hydrogen are formed at STP?

Zn + 2HCl ZnCl2 + H2 79.1 g ? L0.90 L

Limiting Reactants

79.1g Zn

1 molZn

65.39g Zn

= 27.1 L H2

1 molH2

1 molZn

22.4 LH2

1 molH2

Zn + 2HCl ZnCl2 + H2 79.1 g ? L0.90 L

Limiting Reactants

0.90L HCl

1 molHCl

22.4

L HCl

= 0.45 L H2

1 molH2

2 molHCL

22.4 LH2

1 molH2

Zn + 2HCl ZnCl2 + H2 79.1 g ? L0.90 L

Limiting Reactants

Zn: 27.1 L H2 HCl: 0.45 L H2

Limiting reactant: HCl

Excess reactant: Zn

Percent Yield

Percent yield- the ratio of the actual yield to the theoretical yield

Actual yield- the amount of product formed when a reaction is carried out in the laboratory

Theoretical yield- the calculated amount of product formed during a reaction

Percent Yield

100yield ltheoretica

yield actualyield %

calculated on paper

measured in lab

Percent Yield

When 45.8 g of K2CO3 react with excess

HCl, 46.3 g of KCl are formed. Calculate the theoretical and % yields of KCl.

K2CO3 + 2HCl 2KCl + H2O + CO2

45.8 g ? g

actual: 46.3 g

Mole - MoleKnown mol of unknown

mol of known

Mol Ratio – from equationMass - Mass

Known g

molar mass known

1 mol known mol of unknown

mol of known 1 mol unknown

molar mass unknown

Known L

22.4 L known

1 mol known mol of unknown

mol of known 1 mol unknown

22.4 L unknown

particles

6.02 × 1023 particles

6.02 × 1023 particles

OROR

OR

Other

Formulas to Use