# Chapter 9 Pages 274 - 299. Proportional Relationships u I have 5 eggs. How many cookies can I make? 3/4 c. brown sugar 1 tsp vanilla extract 2 eggs 2.

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Chapter 9 Pages 274 - 299

Proportional Relationships u I have 5 eggs. How many cookies can I make? 3/4 c. brown sugar 1 tsp vanilla extract 2 eggs 2 c. chocolate chips Makes 5 dozen cookies. 2 1/4 c. flour 1 tsp. baking soda 1 tsp. salt 1 c. butter 3/4 c. sugar 5 eggs5 doz. 2 eggs = 12.5 dozen cookies Ratio of eggs to cookies

Stoichiometry u Composition stoichiometry – the mass relationships between elements in compounds (determined by the subscript) u Al 2 O 3 contains two moles of aluminum and 3 moles of oxygen

Reaction Stoichiometry u Reaction stoichiometry – the mass relationships between reactants and products in a chemical reaction u All reaction stoichiometry starts with a balanced chemical equation.

Mole Ratios u A mole ratio is a conversion factor that relates the amounts in moles of any two substances in a chemical reaction. u indicated by coefficients in a balanced equation

Mole Ratios  2 Al 2 O 3  Al + 3O 2 u 2 moles of Al 2 O 3 produces 3 moles of O 2 and 4 moles of aluminum 2 moles Al 2 O 3 3 mole O 2 or 2 moles Al 2 O 3 3 mole O 2 2 moles Al 2 O 3 4 mole Al 2 moles Al 2 O 3 or ? ?

Stoichiometry Problems u How many grams of silver will be formed from 12.0 g copper? 12.0 g Cu 1 mol Cu 63.55 g Cu = 40.7 g Ag Cu + 2AgNO 3  2Ag + Cu(NO 3 ) 2 2 mol Ag 1 mol Cu 107.87 g Ag 1 mol Ag 12.0 g? g

Mole to Mole conversions Moles of known X Mole Ratio = Moles of unknown

Mole to Mole conversions u How many moles of O 2 are produced when 3.34 moles of Al 2 O 3 decompose?

Mole to Mass conversions Moles of known X Mole Ratio X Molar Mass of unknown = Mass of unknown

Mole to Mass Conversions u What mass of glucose is produced when 3.00 moles of water react during photosynthesis?

Mass to Mole conversions Mass of known X Mole Ratio X 1 Molar Mass known = Moles of unknown

Mass to Mole Conversion u If 73.7 grams of propane are burned, how many moles of oxygen are consumed?

Mass to Mass conversions Mass of known X Mole Ratio X 1 Molar Mass known = Mass of unknown X Molar Mass of unknown

For Example u The U. S. Space Shuttle boosters use this reaction  3 Al(s) + 3 NH 4 ClO 4  Al 2 O 3 + AlCl 3 + 3 NO + 6H 2 O u How much Al must be used to react with 652 g of NH 4 ClO 4 ? u How much water is produced? u How much AlCl 3 ?

Other Conversions u Liters of a gas to moles u At STP u 25ºC and 1 atmosphere pressure u At STP 22.4 L of a gas = 1 mole u If 6.45 moles of water are decomposed, how many liters of oxygen will be produced at STP?

For Example u If 6.45 grams of water are decomposed, how many liters of oxygen will be produced at STP?  H 2 O  H 2 + O 2 6.45 g H 2 O 18.02 g H 2 O 1 mol H 2 O 2 mol H 2 O 1 mol O 2 22.4 L O 2

Example u How many liters of CO 2 at STP will be produced from the complete combustion of 23.2 g C 4 H 10 ? u What volume of oxygen will be required?

You work in a sandwich shop. You MUST make sandwiches according to the following formula: You use two pieces of bread, 4 pieces of meat, 2 pieces of cheese, 3 pieces of bacon and 2 ounces of special sauce. If you have 20 pieces of bread, 32 pieces of meat, 20 pieces of cheese, 21 pieces of bacon and one quart of special sauce, how many sandwiches can you make? Learning Log

Limiting Reactants u Available Ingredients 4 slices of bread 1 jar of peanut butter 1/2 jar of jelly u Limiting Reactant bread u Excess Reactants peanut butter and jelly

Limiting Reactants u Limiting Reactant used up in a reaction determines the amount of product u Excess Reactant added to ensure that the other reactant is completely used up cheaper & easier to recycle Or happens naturally in nature

Example u Calcium hydroxide is a base used to neutralize acid spills. If you have 6.3 mol of hydrochloric acid and you put 2.8 mol of calcium hydroxide on it, which substance is the limiting reactant. u How many moles of the excess reactant remain?

Practice u Workbook samples p. 115, 118 u Practice handout

Percent Yield calculated on paper measured in lab

Example u 6.78 g of copper is produced when 3.92 g of Al are reacted with excess copper (II) sulfate.  2Al + 3 CuSO 4  Al 2 (SO 4 ) 3 + 3Cu u What is the actual yield? u What is the theoretical yield? u What is the percent yield?

Details u Percent yield tells us how “efficient” a reaction is. u Percent yield can not be bigger than 100 %.

Vocabulary Review

u Involves the mass relationships between reactants and products in a chemical reaction

Reaction stoichiometry

u The reactant that is used up completely in a chemical reaction and therefore determines the amount of product that can be obtained

Limiting reactant

u Relates the amount in moles of any two substances involved in a chemical reaction

Mole ratio

u The maximum amount of product that can be obtained u ( It is calculated by stoichiometry)

Theoretical yield

u The mass in grams of one mole of a pure substance

Molar mass

u The ratio of the actual yield to the theoretical yield multiplied by 100 u (Will be less than 100 because actual yield is always less than theoretical)

Percent yield

u Deals with the mass relationships of elements in compounds

Composition stoichiometry

u The measured amount of product obtained in a chemical reaction

Actual yield

u The substance that is not used up completely in a chemical reaction u (some will remain)

Excess reactant

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