# Chapter 12: Stoichiometry

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Chapter 12: Stoichiometry
Mr. Samaniego Lawndale High

Problem 12.2 (moles of product)
How many moles of ammonia are produced when mol of nitrogen reacts with hydrogen? mol = ? (NH3) 0.60 mol N2 N H NH3 3 2 0.60 mol N2 = 1.2 mol NH3

12.1 The Arithmetic of Equations
Balanced equations are necessary to find the amount of product or reactant needed in a chemical reaction. Cu + O2 CuO

Problem 12.3 (mass of product)
Calculate the number of grams of NH3 produced by the reaction of 5.40 g of hydrogen with an excess of nitrogen. The balanced equation is N H NH3 3 2 mass = ? (NH3) 5.40 g H2 5.40 g H2 = 30.4 g NH3

Example Problem (p. 379, 44) Li3N + 3H2O NH3 + 3LiOH
Lithium nitride reacts with water to form ammonia and aqueous lithium hydroxide. Li3N + 3H2O NH3 + 3LiOH a. What mass of water is needed to react with 32.9 g of Li3N? b. When the above reaction takes place, how many molecules of NH3 are produced? c. Calculate the number of grams of Li3N that must be added to an excess of water to produce 15.0 L of NH3 (at STP).

Class work Pages : (skip 11a). (12/14/11, 12/15/11)

Generic Solutions A + B C grams of A to grams of C:
grams A  mol A  mol C  grams C mol of A to grams of C: mol A  mol C  grams C mol of A to mol of C: mol A  mol C grams of A to mol of C: grams A  mol A  mol C

Problem 36 b (mass of product)
Calculate the number of grams of H2O produced by the reaction of 12.5 g of nitrogen monoxide with an excess of ammonia. The balanced equation is 4NH3 + 6NO N2 + 6H2O mass = ? (H2O) 12.5 g NH3 12.5 g NH3 = 19.8 g H2O

Problem 12.4 (molecules of product)
After Ch 12 Quiz How many molecules of oxygen are produced when g of water is decomposed by electrolysis according to this balanced equation? 2H2O H O2 molecules = ? (O2) 29.2 g H2O 29.2 g H2O = 4.88x1023 molecules O2

Problem 12.5 (vol-vol stoichiometry)
Nitrogen monoxide and oxygen gas combine to form the brown gas nitrogen dioxide, which contributes to photochemical smog. How many liters of nitrogen dioxide are produced when 34 L of oxygen reacts with an excess of nitrogen monoxide? STP.) vol O2 = 34 L vol = ? (NO2) 2NO + O NO2 34 L O2 Remember: 1 mol = 22.4 L @STP = 68 L NO2

Problem 12.6 (vol stoichiometry)
Assuming STP, how many milliliters of oxygen are needed to produce 20.4 mL SO3 according to this balanced equation? 2SO2 + O SO3 vol SO3 = 20.4 mL vol = ? (mL O2) Remember: 1 mol = 22.4 L @STP 20.4 mL SO3 = 10.2 mL O2