1. STOICHIOMETRY

2.  Stoichiometry is the science of using balanced chemical equations to determine exact amounts of chemicals needed or produced in a chemical reaction.

3. Determining Ratios in Balanced Chemical Reactions  What is the balanced chemical reaction for the reaction between nitrogen gas (N 2 ) and hydrogen gas (H 2 ) to produce ammonia (NH 3 )?  This means that for every one mole of N 2 you have (28.02 g) you need to have 3 mole of H 2 (3 × 2.02 g = 6.06 g)… (34.08 g of reactants)  You make 2 mole of NH 3 ( 14.01 + 3.03 = 17.04 * 2 = 34.08 g)

4. Mole Ratios  These are what we call mole ratios  Example 1: If you had 5 mol of N 2, how many mol of H 2 would you need? How many mol of NH 3 would you make?

5. Example Problem 2: Calculations Involving Mass of Reactants  Propane, C 3 H 8(g), is a gas that is commonly used in barbeques. Calculate the mass of oxygen gas, O 2, that is needed to burn 15 g of propane. (Produces CO 2 and H 2 O)

6. Example Problem 2: Calculations involving Numbers of Entities and Mass  How many molecules of oxygen are produced from the decomposition of 12 g of water into its elements?  Recall: O 2 and H 2 are produced

7. Practice Problems: 1. Bauxite ore contains aluminum oxide, Al 2 O 3, which is decomposed using electricity to produce aluminum metal and oxygen gas (O 2 ). What masse of aluminum metal can be produced from 125 g of aluminum oxide? How many grams of O 2 are produced? 2. Potassium metal, K (s), reacts with hydrochloric acid, HCl (aq), to produce aqueous potassium chloride and hydrogen gas, H 2. How many grams of potassium are required to produce 5.00 g of hydrogen gas? 3. Potassium chlorate, KClO 3, decomposes when heated to form solid potassium chloride and oxygen gas. How many grams of KClO 3 must decompose to produce 0.96 g of O 2 ?

9. Limiting Reactant, Excess Reactant and Percent Yield  In the real world, you never have perfect amounts of every reactant you need…

10. Example  In the synthesis of water, we require exactly 2 mol of H 2 and exactly 1 mol O 2 to create exactly 2 mol of H 2 O…  What would happen if we have a 2 mol H 2 and 8 mol of O 2 ?  Would this change the amount f H 2 O that would be created?

11.  No…  There would be 7mol of O 2 left over.  O 2 is an excess reagent; H 2 is limiting

12. Balanced Equation 2 H 2 O2O2 2H 2 O Moles212 Molar Mass2.02 g/mol32.00 g/mol18.02 g/mol Mass4.04 g32.00 g36.04 g

13. Balanced Equation 2 H 2 O2O2 2H 2 O Moles282 Molar Mass2.02 g/mol32.00 g/mol18.02 g/mol Mass (Needed)4.04 g32.00 g Mass (Used Up/Made) 4.04 g32.00 g36.04 Left Over0.00 g224.00 g

14.  A chemical reaction will stop once any one of the reactants runs out.  This reactant is known as the limiting reagent (limiting reactant)  Any other reactant is an excess reagent

15. Example 1: Table Salt, BaCL, can be formed by the reaction of sodium metal and chlorine gas. A reaction mixture contains 45.9 g of sodium and 142.0 g of chlorine. Calculate the mass of sodium chloride that is produced.

16. Example 2:  Determine the mass of carbon monoxide that is produced when 32.1 g of methane, CH 4 undergoes incomplete combustion with 160.0 g of oxygen (products: CO and H 2 O)

17. Example 3:  Phosphorus, P 4, reacts with chlorine gas to produce solid phosphorus pentachloride as the only product. Determine the mas of phosphorus pentachloride that is produced from a reaction between 123.88 g of phosphorus and 950.00 g of chlorine.

18. Percentage Yield  Yield: the quantity of product produced in a chemical reaction  Actual Yield: the quantity of product that is actually produced in a chemical reaction  Theoretical Yield: the quantity of product calculated from a balanced chemical equation (using stoichiometry)

19.  There are many reasons why the amount of a product predicted for a reaction may not actually form  Reactions may not go to completion  Some of the reactant may be impure  There may be competing side reactions  It may be difficult to collect the product

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21. Example 1:  Iron is produced from its ore, hematite, Fe 2 O 3, by heating hematite with carbon monoxide in a blast furnace. If 635 g of iron is obtained from 1150 g of hematite, what is the percentage yield of iron?

22. Practice 1:  The most common ore of arsenic, FeSAs, can be heated to produce arsenic and iron(II) sulfide. When 250 g of the ore was processed industrially, 95.3 kg of arsenic was obtained. Calculate the yield of arsenic.

23. Homework…  You have a test on Monday, November 24 at 6:30 pm, sharp.  I strongly recommend you study for it.