Stoichiometry Table of Contents Section 1 Introduction to Stoichiometry Section 2 Ideal Stoichiometric Calculations Section 3 Limiting Reactants and Percentage Yield
Section 1 Introduction to Stoichiometry Objective Define stoichiometry. Describe the importance of the mole ratio in stoichiometric calculations. Write a mole ratio relating two substances in a chemical equation.
Section 1 Introduction to Stoichiometry Stoichiometry Definition Composition stoichiometry (chapter 3) deals with the mass relationships of elements in compounds Reaction stoichiometry involves the mass relationships between reactants and products in a chemical reaction
Section 1 Introduction to Stoichiometry Mole Ratio Mole Ratio - conversion factor that relates the amounts in moles of any two substances involved in a chemical reaction Example: 2Al 2 O 3 (l) 4Al(s) + 3O 2 (g) Mole Ratios: 2 mol Al 2 O 3 2 mol Al 2 O 3 4 mol Al,, 4 mol Al 3 mol O 2 3 mol O 2
Section 1 Introduction to Stoichiometry Converting Between Amounts in Moles
Questions: What is Stoichiometry? Write all the possible mole ratios for the following equations: 2HgO 2Hg and O 2 4NH 3 + 6NO 5N 2 + 6H 2 O How is a mole ratio used in stoichiometry? What step must be performed before any stoichiometry problem is solved? Why?
Section 2 Ideal Stoichiometric Calculations Lesson Starter Acid-Base Neutralization Reaction Demonstration What is the equation for the reaction of HCl with NaOH? What is the mole ratio of HCl to NaOH?
Section 2 Ideal Stoichiometric Calculations Objective Calculate the amount in moles of a reactant or a product from the amount in moles of a different reactant or product. Calculate the mass of a reactant or a product from the amount in moles of a different reactant or product. Calculate the amount in moles of a reactant or a product from the mass of a different reactant or product. Calculate the mass of a reactant or a product from the mass of a different reactant or product.
Section 2 Ideal Stoichiometric Calculations Conversions of Quantities in Moles Sample Problem A In a spacecraft, the carbon dioxide exhaled by astronauts can be removed by its reaction with lithium hydroxide, LiOH, according to the following chemical equation. CO 2 (g) + 2LiOH(s) Li 2 CO 3 (s) + H 2 O(l) How many moles of lithium hydroxide are required to react with 20 mol CO 2, the average amount exhaled by a person each day?
Section 2 Ideal Stoichiometric Calculations Conversions of Quantities in Moles Sample Problem A Solution CO 2 (g) + 2LiOH(s) Li 2 CO 3 (s) + H 2 O(l) Given: amount of CO 2 = 20 mol Unknown: amount of LiOH (mol) Solution: mol CO 2 20 mol CO 2 mol ratio mol LiOH mol LiOH mol CO 2 2 mol LiOH 40 mol LiOH 1 mol CO 2
Questions: How many moles of ammonia are produced when 6 moles of hydrogen gas react with excess nitrogen? How many moles of potassium chlorate are needed to produce 15 moles of oxygen?
Section 2 Ideal Stoichiometric Calculations Conversions of Amounts in Moles to Mass
Section 2 Ideal Stoichiometric Calculations Solving Stoichiometry Problems with Moles or Grams
Section 2 Ideal Stoichiometric Calculations Conversions of Amounts in Moles to Mass Sample Problem B In photosynthesis, plants use energy from the sun to produce glucose, C 6 H 12 O 6, and oxygen from the reaction of carbon dioxide and water. What mass, in grams, of glucose is produced when 3.00 mol of water react with carbon dioxide?
Section 2 Ideal Stoichiometric Calculations Conversions of Amounts in Moles to Mass Sample Problem B Solution Given: amount of H 2 O = 3.00 mol Unknown: mass of C 6 H 12 O 6 produced (g) Solution: Balanced Equation: 6CO 2 (g) + 6H 2 O(l) C 6 H 12 O 6 (s) + 6O 2 (g) mol ratio molar mass factor mol H 2 O mol C 6 H 12 O 6 mol H 2 O g C 6 H 12 O 6 mol C 6 H 12 O 6 g C 6 H 12 O 6 3.00 mol H 2 O 1 mol C 6 H 12 O 6 6 mol H 2 O 180.18 g C 6 H 12 O 6 1 mol C 6 H 12 O 6 = 90.1 g C 6 H 12 O 6
Questions: When magnesium burns in air, what mass of magnesium oxide is produced from 2.0 moles of magnesium burning? What mass of glucose (C 6 H 12 O 6 ) can be produced from photosynthesis of 10 moles of CO 2?
Section 2 Ideal Stoichiometric Calculations Conversions of Mass to Amounts in Moles
Section 2 Ideal Stoichiometric Calculations Conversions of Mass to Amounts in Moles Sample Problem D The first step in the industrial manufacture of nitric acid is the catalytic oxidation of ammonia. NH 3 (g) + O 2 (g) NO(g) + H 2 O(g) (unbalanced) The reaction is run using 824 g NH 3 and excess oxygen. a. How many moles of NO are formed? b. How many moles of H 2 O are formed?
Section 2 Ideal Stoichiometric Calculations Conversions of Mass to Amounts in Moles Sample Problem D Solution Given: mass of NH 3 = 824 g Unknown: a. amount of NO produced (mol) b. amount of H 2 O produced (mol) Solution: Balanced Equation: 4NH 3 (g) + 5O 2 (g) 4NO(g) + 6H 2 O(g) a. molar mass factor g NH 3 mol NH 3 g NH 3 mol ratio mol NO mol NH 3 mol NO b. g NH 3 mol NH 3 g NH 3 mol H 2 O mol NH 3 mol H 2 O
Section 2 Ideal Stoichiometric Calculations Conversions of Mass to Amounts in Moles Sample Problem D Solution, continued molar mass factor mol ratio a. 824 g NH 3 1 mol NH 3 17.04 g NH 3 4 mol NO 4 mol NH 3 48.4 mol NO b. 824 g NH 3 1 mol NH 3 6 mol H O 2 72.5 mol H 17.04 g NH 3 4 mol NH 2 O 3
Section 2 Ideal Stoichiometric Calculations Solving Mass-Mass Problems
Section 2 Ideal Stoichiometric Calculations Mass-Mass to Calculations Sample Problem E Tin(II) fluoride, SnF 2, is used in some toothpastes. It is made by the reaction of tin with hydrogen fluoride according to the following equation. Sn(s) + 2HF(g) SnF 2 (s) + H 2 (g) How many grams of SnF 2 are produced from the reaction of 30.00 g HF with Sn?
Section 2 Ideal Stoichiometric Calculations Mass-Mass to Calculations Sample Problem E Solution Given: amount of HF = 30.00 g Unknown: mass of SnF 2 produced (g) Solution: g HF g HF molar mass factor mol ratio molar mass factor mol HF g HF mol SnF 2 mol HF g SnF 2 mol SnF 2 g SnF 2 1 mol HF 20.01 g HF 1 mol SnF 2 2 mol HF 156.71 g SnF 2 1 mol SnF 2 = 117.5 g SnF 2
Section 2 Ideal Stoichiometric Calculations Solving Various Types of Stoichiometry Problems
Section 2 Ideal Stoichiometric Calculations Solving Various Types of Stoichiometry Problems
Section 2 Ideal Stoichiometric Calculations Solving Volume-Volume Problems
Section 2 Ideal Stoichiometric Calculations Solving Particle Problems
Questions: Ammonium nitrate decomposes into dinitrogen monoxide and water, how many grams of ammonium nitrate are required to produce 33g of dinitrogen monoxide and how many grams of water are produced? When copper is added to silver nitrate, silver and copper(ii) nitrate are produced. What mass of silver is produced from 100g of copper? What mass of aluminum is produced by the decomposition of 5kg of aluminum oxide? Ammonia mixed with oxygen produces nitrogen and water. Given 4 moles of NH 3 how much is there of everything else Given 4 moles of N 2 how much is there of everything else Given 4.5 moles of O 2 how much is there of everything else
More Questions: Magnesium and hydrochloric acid are combined what mass of HCl is needed to completely react with 2.5 moles of magnesium? What mass of each product is produced? CaC 2 + 2H 2 O C 2 H 2 + Ca(OH) 2 If 32 g of calcium carbide are consumed how many moles of water are needed? How many moles of each product are produced? When sodium chloride reacts with silver nitrate silver chloride precipitates. What mass of silver chloride is produced from 75 g of silver nitrate? What mass of carbon and oxygen are needed to make 56 g of carbon monoxide?
Section 3 Limiting Reactants and Percentage Yield Objectives Describe a method for determining which of two reactants is a limiting reactant. Calculate the amount in moles or mass in grams of a product, given the amounts in moles or masses in grams of two reactants, one of which is in excess. Distinguish between theoretical yield, actual yield, and percentage yield. Calculate percentage yield, given the actual yield and quantity of a reactant.
Section 3 Limiting Reactants and Percentage Yield Limiting Reactants Limiting Reactant - reactant that limits the amount of the other reactant that can combine and the amount of product that can form in a chemical reaction Excess Reactant - substance that is not used up completely in a reaction
Section 3 Limiting Reactants and Percentage Yield Limited Reactants Sample Problem F Silicon dioxide (quartz) is usually quite unreactive but reacts readily with hydrogen fluoride according to the following equation. SiO 2 (s) + 4HF(g) SiF 4 (g) + 2H 2 O(l) If 6.0 mol HF is added to 4.5 mol SiO 2, which is the limiting reactant?
Section 3 Limiting Reactants and Percentage Yield Limited Reactants Sample Problem F Solution SiO 2 (s) + 4HF(g) SiF 4 (g) + 2H 2 O(l) Given: amount of HF = 6.0 mol amount of SiO 2 = 4.5 mol Unknown: limiting reactant Solution: mole ratio mol HF mol SiF 4 mol HF mol SiO 2 mol SiF 4 mol SiO 2 mol SiF 4 produced mol SiF 4 produced
Section 3 Limiting Reactants and Percentage Yield Limited Reactants Sample Problem F Solution, continued SiO 2 (s) + 4HF(g) SiF 4 (g) + 2H 2 O(l) 6.0 mol HF 1 mol SiF 4 4 mol HF 1.5 mol SiF 4 produced 4.5 mol SiO 2 1 mol SiF 4 1 mol SiO 2 4.5 mol SiF 4 produced HF is the limiting reactant.
Example Carbon reacts with steam at high temperatures to produce hydrogen and carbon monoxide. If 2.4 moles of carbon are exposed to 3.1 moles of steam, what is the limiting reactant? How much of the excess reactant is left over? How many moles of each product are formed?
Questions: N 2 H 4 + 2 H 2 O 2 N 2 + 4 H 2 O Which is the limiting reactant when 0.75 mol N 2 H 4 is mixed with 0.5 mol H 2 O 2? How much of the excess, in moles, remains? How much of each product, in moles, is produced? 8Zn + S 8 8ZnS Which is the limiting reactant when 2 mol Zn is mixed with 1 mol S 8? How much of the excess, in moles, remains? How much product, in moles, is produced?
Section 3 Limiting Reactants and Percentage Yield Percentage Yield Theoretical Yield - maximum amount of product that can be produced from a given amount of reactant Actual Yield - measured amount of that product obtained from a reaction Percent Yield - ratio of the actual yield to the theoretical yield, multiplied by 100 percentage yield actual yield theorectical yield 100
Visual Concepts Comparing Actual and Theoretical Yield Click below to watch the Visual Concept. Visual Concept
Section 3 Limiting Reactants and Percentage Yield Percentage Yield Sample Problem H Chlorobenzene, C 6 H 5 Cl, is used in the production of many important chemicals, such as aspirin, dyes, and disinfectants. One industrial method of preparing chlorobenzene is to react benzene, C 6 H 6, with chlorine, as represented by the following equation. C 6 H 6 (l) + Cl 2 (g) C 6 H 5 Cl(l) + HCl(g) When 36.8 g C 6 H 6 react with an excess of Cl 2, the actual yield of C 6 H 5 Cl is 38.8 g. What is the percentage yield of C 6 H 5 Cl?
Section 3 Limiting Reactants and Percentage Yield Percentage Yield Sample Problem H Solution C 6 H 6 (l) + Cl 2 (g) C 6 H 5 Cl(l) + HCl(g) Given: mass of C 6 H 6 = 36.8 g mass of Cl 2 = excess actual yield of C 6 H 5 Cl = 38.8 g Unknown: percentage yield of C 6 H 5 Cl Solution: Theoretical yield molar mass factor mol ratio molar mass g C 6 H 6 mol C 6 H 6 g C 6 H 6 mol C 6 H 5 Cl mol C 6 H 6 g C 6 H 5 Cl mol C 6 H 5 Cl g C 6 H 5 Cl
Section 3 Limiting Reactants and Percentage Yield Percentage Yield Sample Problem H Solution, continued C 6 H 6 (l) + Cl 2 (g) C 6 H 5 Cl(l) + HCl(g) Theoretical yield 1 mol C 36.8 g C 6 H 6 6 H 6 1 mol C H Cl 6 5 112.56 g C H Cl 6 5 78.12 g C 6 H 6 1 mol C 6 H 6 1 mol C 6 H 5 Cl Percentage yield 53.0 g C 6 H 5 Cl percentage yield C 6 H 5 Cl percentage yield 38.8 g 53.0 g actual yield theorectical yield 100 100 73.2%
Examples: CO + 2H 2 CH 3 OH If 75g of CO reacts to produce 68.4g CH 3 OH what is the percent yield? Al + CuSO 4 Al 2 (SO 4 ) 3 + Cu If 1.85g of Al react and the percent yield of Cu is 56.6%, what mass of Cu is produced
Assignment: CS 2 + 3O 2 CO 2 + SO 2 If 1 moles of CS 2 is exposed to 1 mole of O 2, what is the limiting reactant? How much of the excess reactant is left over? How many moles of each product are formed? Mg + H 2 O Mg(OH) 2 + H 2 If 16.2 grams of magnesium are exposed to 12.0 grams of water, what is the limiting reactant? How much of the excess reactant is left over? How many grams of each product are formed? CaCO 3 CaO + CO 2 When 2 x 103g CaCO 3 are heated the actual yield of CaO is 1.05 X 103g. What is the percent yield?