Limiting Reactant II and Percent Yield

A.K.A. Stoichiometry

The reactant that limits the amount of product produced

Limiting reactant is consumed fully in a chemical reaction

Excess reactant remains in a chemical reaction

What is a Limiting Reactant?

Remember The Sundae Example…

The chocolate syrup was consumed fully.The ice cream and cherries are left over.

Calculate using mass-mass conversion; find which reactant produces the least amount of product

Or use mole-mole conversion to determine which reactant is consumed first

How do we determine which reactant is the limiting

reactant?

What is the limiting reactant when 10.0 g of SiO2 react with 5.0 g of HF?

Create a conversion pathway using mass-mass conversion

SiO2(s) + 4 HF(l) → SiF4(g) + 2 H2O(l)

SiO2(s) + 4 HF(l) → SiF4(g) + 2 H2O(l)

SiO2 is the limiting reactant!

Limiting Reactant RelayTime for

How efficient is a chemical reaction?

Does the reaction go to completion?

How much product is produced?

How can we predict the amount of product produced?

How Does Sundae Production and Percent Yield Relate?

• If you made only 25 sundaes but You really needed 40, what was

your production yield?• Actual yield = 25 sundaes• Production (theoretical) yield = 40

sundaes• Percent yield = 25 x 100 % =

63% 40

5.00 g of Cu is mixed with an excess of AgNO3.

The reaction produces 15.2 g of Ag

What is the percent yield for this reaction?

We want to know how much product is produced?

Create your conversion pathway using mass-mass conversion

Cu + 2 AgNO3 2 Ag + Cu(NO3)2

17.0 g Ag is our theoretical yield; need to use it to calculate percent yield

Percent Yield

Percent Yield = Actual yield x 100

Theoretical yield

Actual/Theoretical

Percent Percent Yield

Percent Yield = 15.2 g Ag x 100 = 89.4 %

17.0 g Ag

Percent Yield WorksheetYour turn…

What is the percent yield when 24.8 g of CaCO3 decomposes to give 13.1 g CaO? CaCO3CaO + CO2

Plan your conversion pathwayUtilize mass-mass conversion

One more example

CaCO3CaO + CO2

The theoretical yield is 13.9 g of CaO; what is our percent yield? The reaction made 13.1 g CaO

Actual/Theoretical

Percent Percent Yield

= 13.1 g x 100 = 94.2 %

13.9 g

Exit TicketTime to fill out an

Read over Stoichiometry Lab carefully

Answer pre-laboratory questions

Homework