1. Chapter 11: Stoichiometry

2. Particle and Mole Relationships
Chemical reactions stop when one of the reactants is used up
Stoichiometry: the study of quantitative relationships between the amounts of reactants used and amounts of products formed by a chemical reaction
The amount of each reactant present at the start of a chemical reaction determines how much product can form
Based on the law of conservation of mass
Matter is neither created or destroyed in a chemical reaction
Therefore, mass of reactants = mass of products

3. Evidence of the Law of Conservation of Mass

4. Mole Ratio
Mole Ratio: ratio between the numbers of moles of any two substances in a balanced chemical reaction
Can be used as a conversion factor in calculations
The number of mole ratios that can be written for any equation is (n)(n-1) where n is the number of species in the chemical reaction
The coefficients in a chemical equation indicate the relationship between mole of reactants and products

5. Mole Ratio
____K(s) + ____Br2 (l)  ____KBr(s) Find the ratio between bromine and potassium bromide How many mole ratios can be written for this reaction?

6. Stoichiometry Calculations
____Al(s) + ____O2 (g)  ____Al2O3
How many grams of Al are needed to completely react with 2.4 mol of O2?

7. Key points to remember:
Must have a balanced reaction
Coefficients represent moles
Only go to the reaction once for a conversion

8. ____VO + ____Fe2O3  ____FeO + ____V2O5
How many grams of Fe2O3 are needed to produce 90.5 g of FeO?

9. Limiting Reactant
Reactions proceed until one of the reactants is used up and one is left in excess
Limiting Reactant: limits the extent of the reaction and thereby, determine the amount of product formed
Excess Reactant: all the leftover, unused reactants
**Determining the limiting reactant is important because the amount of the product formed depends on this reactant

11. Determining the Limiting Reactant
Method #1
Calculate the final mass of a product from both reactant quantities and determine which is the limiting reactant based on the least amount of product formed
Solve any additional questions using the limiting reactant quantity as the starting point
Method #2
Calculate the number of moles for each reactant
Divide moles of reactant by the coefficient of the balanced equation. The substance with the smaller answer is the limiting reactant

12. ___SO2 + ___CaCO3 + ___O2  ___CaSO4 + ___CO2
What is the limiting reactant when 95.0 g of SO2 and 100 g of CaCO3 are added to excess O2?
How many g of CO2 are formed in the reaction?
How many grams of excess remain?

13. Percent Yield Percent Yield = x 100
Theoretical Yield: the maximum amount of product that can be produced from a given amount of reactant
Actual Yield: the amount of product produced when the chemical reaction is carried out in an experiment
Percent Yield: the ratio of the actual yield to the theoretical yield expressed as a percent
Actual yield
Theoretical yield
Percent Yield =
x 100

14. Calculating Percent Yield
You calculate the theoretical yield of a chemical reaction starting with 50.0g of reactant is 25.0g of product. What is the percent yield if the actual yield is 22.0g of product?

15. Why a percent is less than 100%
Reactions do not always go to completion
Impure reactants
Some product can be lost in the recovery process

16. Percent Yield ____KClO3  ____KCl + ____O2
A 95.8 g sample of KClO3 is heated in the lab and 20.1 g of KCl is recovered. What is the % yield of this process?