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Stoichiometry Notesheets Name________________________________ The Mathematics of Chemical Equations Period______Date______________________ 9.1: Balanced Chemical Equations 1. Provides qualitative and quantitative information. 2. Supports the Law of ____________________________________________________ 3. 2H2 + O2 → 2H2O The above equation is interpreted in terms of particles as follows: A. _____________________ of H2 react with _________________ of O2 to produce _______________________ of water. The ratio of H2 to O2 to water is ___________. Or B. 20 molecules of H2 react with _______ molecules of O2 to produce _______ molecules of water. The ratio of H2 to O2 to water is ________________. C. The original equation can then be interpreted as follows: 2 moles of H2 react with _______ mole of O2 to produce ______ moles of water. The ratio of H2 to O2 to water is ________________. D. It is more convenient to interpret the coefficients as the number of moles, because we measure amounts of substances by _______________ in the laboratory. We can convert between grams and moles in solving problems involving chemical reactions. 4. Stoichiometry: The study of the ________________________________________________________ that exist in a formula and in a chemical reaction. 5. The word Stoichiometry comes from the Greek word “stoicheion” meaning ______________________, and “metron”, meaning __________________________. 6. Importance: The safe, economical and ____________________________ manufacture of chemicals (or food) and the safe administration of pharmaceuticals. 7. Proof: The Law of Conservation of Mass is shown by the ______________________ equation, or by adding up all the masses of reactants and products to determine if they are equal. 1 8. Mole-Mole Problems require 3 steps to determine the molar ratio: Stoichiometryville Map A. _______________________________ B. _________________________________________________________________________ C. _________________________________________________________________________ Ex #1) Ammonium nitrate decomposes into dinitrogen monoxide and water. How many moles of dinitrogen monoxide and water are produced from 2.25 moles of reactants? Equation: Ratio: 2.25 mol NH4NO3 2.25 mol NH4NO3 Ex #2) Hydrochloric acid reacts with zinc in a single replacement reaction. How many moles of hydrochloric acid are needed to react with 2.3 moles of Zn? Equation: Ratio: Stoichiometry Problems: 1. A balanced equation represents a chemical reaction that conforms to the ______________________________________________________________________ 2. _________________________ can NEVER be changed to balance a chemical equation. 3. The total ____________ of the reactants is the same as the total ____________ of the products. 4. Coefficients in a balanced equation relate _______________ of substances in the reaction. 5. Coefficients are used in constructing the _____________ ____________ for a stoichiometric problem. 2 6. Grams of the known must first be converted to ______________, then use the ________________ _____________ to relate the 2 substances, finally convert the moles of the unknown to ____________. 7. Mass-Mass Problems: Ex #1) What mass of aluminum oxide can be prepared by the reaction of 67.5 g of Al and oxygen? Ex #2) Glucose is used as an energy source by the human body. Calculate the number of grams of oxygen needed to oxidize (burn) 12.5 g of glucose. Write the balanced combustion reaction: C6H12O6 + O2 → Ex #3) During WWII Germany used a method called the Haber Process to produce ammonia for explosives. Today a similar process is used to make fertilizers. If an excess of nitrogen is reacted with 1.71 mol of hydrogen, how many grams of ammonia, NH3, is produced? Ex #4) Iron will react with oxygen gas to produce iron (III) oxide. How many grams of iron (III) oxide will be produced if 0.18 mol of iron reacts? 3 8. Mass-Volume Problems: Ex) Airbags contain a powder called sodium azide (NaN3). When exposed to a spark the sodium azide quickly decomposes into sodium and nitrogen gas. If an uninflated airbag contains 125 g of NaN3, what volume in liters of nitrogen gas will be produced at STP? NaN3 → 9. Volume –Volume Problems: Ex) What volume in liters of hydrogen gas is needed to react completely with 15.5 L of nitrogen gas to produce ammonia gas (NH3) at STP? 10. Mass-Particles Problems: Ex) How many particles of barium hydroxide are produced from the single replacement reaction of barium and 9.54 g of water? 11. Volume-Particles Problems: Ex) How many liters of hydrogen gas are produced from the single replacement reaction of calcium with 6.09 x1023 molecules of hydrochloric acid? 4 9.2: % Yield 1. Expected Yield: (Theoretical Yield) Amount of _______________ that should be produced based on _____________________________________. 2. Actual Yield: Amount of _________________ actually obtained in the _________________________. 3. % Yield: . % Yield = 4. % Error: % error = expected - actual x 100% = expected Ex) Lauren burned 4.789 g of magnesium . At the end of the experiment she weighed 7.250 g of product. What is the % yield and the % error for these results? • 1st write and balance the equation. • 2nd calculate the expected yield from the equation. • 3rd calculate the % yield and % error from the above data. 5 5. Limiting Reactant The limiting reactant is the _____________________ substance that becomes used up ____________ when a chemical reaction occurs. It controls how ___________________ or how _________________ product can be formed. Ex) If a recipe for 1 cake is: 2 cups flour and your kitchen contains 2 eggs 1 cup sugar 1½Tbls. baking powder 1 cup water ⅓ cup oil 7 cups flour 2 dozen eggs 9 cups sugar 10 Tbls. baking pwdr unlimited water 3⅓ cups oil How many cakes can you make given the ingredients present in your kitchen? _______ What ingredient is the limiting reactant? __________________ How many eggs are left over after making the cakes? ___________ 6. Look at the following reaction: NH3 + O2 → NO + H2O. In an experiment, 3.25 g of NH3 are reacted with 3.50 g of O2. How many grams of NO are formed? What is the most NO that can be produced? ___________________ Which reactant is the limiting reagent? ____________________ 6