Main Ideas The amount of each reactant present at the start of a chemical reaction determines how much product can form. The solution to every stoichiometric problem requires a balanced chemical equation. Percent yield is a measure of the efficiency of a chemical reaction.
10.1 Defining Stoichiometry: Objectives •Describe the types of relationships indicated by a balanced chemical equation. •State the mole ratios from a balanced chemical equation.
StoichiometryStoichiometry is the study of quantitative relationships between the amounts of products formed by a chemical reaction. Based on the law of conservation of mass. Mass of the reactants must equal the mass of the products. Molecules are not necessarily balanced on each side. Atoms, moles and mass do.
Practice Problem #1 C3H8(g) + 5O2(g) 3CO2 + 4H2O(g)Moles:Mass: Molecules are not necessarily balanced on each side. Atoms, moles and mass do.
Mole RatioMole ratio is a ratio between the numbers of moles of any two substances in a balanced chemical equation. The number of mole ratios that can be written for any equation is (n)x(n-1) where n is the number of substances in the chemical reaction.
Practice Problem #2 4Al(s) + 3O2(g) 2Al2O3(s)Mole Ratios: 3Fe(s) + 4H2O(l) Fe3O4 + 4H2(g)Mole Ratios:
Practice Problem #2 2HgO(s) 2Hg(l) + O2(g)Mole Ratios:
QuestionWhich of the following is a correct mole ratio for the following equation?2Al(s) + 3Br2(l) → 2AlBr3(s)A. 2 mol Al : 3 mol BrB. 3 mol Br2 : 2 mol AlC. 2 mol AlBr3 : 1 mol Br2D. 2 mol Br : 2 mol Al
QuestionHow many mole ratios can be written for the following reaction?4H2(g) + O2(g) → 2H2O(l)A. 6B. 4C. 3D. 2
Practice Problems Page 371 #1 and 2 Page 372 #4,5,6,9
10.2 Stoichiometric Calculations Objectives •Listthe sequence of steps used in solving stoichiometric problems. •Solve stoichiometric problems.
Steps to Solving Stoichiometric Problems1. Write a balanced equation2. Determine the starting point of the calculations. 1. If units are mass units, convert to moles.3. Use the correct reaction molar ratio to convert to moles of substance in question.4. Convert moles to requested units if needed.
Practice Problem #3: Moles to MolesWhen burning propane (C3H8), carbon dioxide is produced. How many moles of CO2 are produced when 10.0 mol of C3H8 are burned in excess oxygen?
Practice Problem #3: Moles to MolesCalculate the moles of CS2 and H2S produced when 1.5 mol S8 is used? CH4(g) + S8(s) CS2(l) + H2S(g)
Practice Problem #3: Moles to MolesSulfuric acid (H2SO4) is formed when sulfur dioxide (SO2) reacts with oxygen and water. How many moles of H2SO4 are produced from 12.5 moles of SO2? How many moles of O2 are needed?
Practice Problem #4: Moles to MassSodium chloride is decomposed into the elements sodium and chlorine. How much chlorine gas, in grams is obtained when 2.50 mol of sodium choride are used?
Practice Problem #5: Mass to MassAcid rain (H2SO4) is formed from SO2, O2 and H2O. If 2.5g of SO2 reacts with excess oxygen and water, how much H2SO4 is produced?
QuestionsHow many moles of CO2 will be produced in the following reaction if the initial amount of reactants was 0.50 moles?2NaHCO3 → Na2CO + CO2 + H2OA. 0.25B. 0.3C. 0.5D. 1.0
QuestionsA chemical reaction equation must be ____ in order to make stoichiometric calculations.A. measuredB. controlledC. balancedD. produced
10.3 Limiting Reactant Objectives•Identify the limiting reactant in achemical equation.•Identify the excess reactant, and calculatethe amount remaining after the reaction iscomplete.•Calculate the mass of a product when theamounts of more than one reactant aregiven.
Limiting ReactantThe limiting reactant limits the extent of the reaction. Determine the amount of product formed. A portion of all the other reactants remains after the reaction stops.Excess reactants are the reactants leftover when a reaction stops.
Example Supplies First Aid Kits 500 bandaids 24 bandaids 85 gauze rolls 4 gauze rolls 24 first aid ointments 1 first aid ointment 24 burn sprays 1 burn spray 65 rolls of tape 3 rolls of tape 50 ace bandages 2 ace bandages
Steps to Determining the Limiting Reactant1. Determine moles of reactants.2. Use mole ratios to determine which reactant is limiting.3. Analyze the excess reactant 1. Moles reacted 2. Mass reacted 3. Excess remaining
Practice Problem #6If 200.0g of sulfur reacts with 100.0g of chlorine, what mass of disulfur dichloride is produced? S8(l) + 4Cl2(g) 4S2Cl2(l)
QuestionsThe mass of the final product in a chemical reaction is based on what?A. the amount of excess reactantB. the amount of limiting reactantC. the presence of a catalystD. the amount of O2 present
QuestionsWhat is the excess reactant in the following reaction if you start with 50.0g of each reactant?P4(s) + 5O2(g) → P4O10(s)A. O2B. P4C. Both are equal.D. unable to determine
10.4 Percent Yield Objectives•Calculatethe theoretical yield of achemical reaction from data.•Determine the percent yield for achemical equation.
Theoretical YieldTheoretical yield is the maximum amount of product that can be produced from a given amount of reactant. Assumes that the reaction goes to completion in the forward direction.
Actual YieldActual yield is the amount of product produced when the chemical reaction is carried out in an experiment.
Percent YieldPercent yield is the ratio of the actual yield expressed as a percent. Represents how efficient a reaction is in producing the desired product Percent yield = (actual yield/theoretical yield) x 100 actual yield(exp erimental) %yield = x100% theoretical yield(calculated)
Practice Problem #7Solid silver chromate (AgCrO4) forms when potassium chromate (K2CrO4) is added to a solution containing .500g of silver nitrate (AgNO3). Determine the theoretical yield of Ag2CrO4. Calculate the percent yield if the reaction yields .455g of Ag2CrO4.
Practice Problem #7 AgNO3 + K2CrO4 Ag2CrO4 + ;.500g AgNO3, theoretical yield of Ag2CrO4?percent yield? .455g of Ag2CrO4
QuestionsThe amount of product that can be produced from a given amount of reactants based on stoichiometric calculations is:A. actual yieldB. percent yieldC. theoretical yieldD. stoichiometric yield
QuestionsYou calculate the theoretical yield of a chemical reaction starting with 50.0g of reactant is 25.0g of product. What is the percent yield if the actual yield is 22.0g of product?A. 88%B. 44%C. 50%D. 97%
10.4 Accumulating Content •Apply knowledge and skills from previous units to content learned in this unit.
Practice Problem #8When an antacid tablet dissolves in water, the fizz isdue to a reaction between sodium hydrogen carbonate(baking soda), also called sodium bicarbonate, andcitric acid (H3C6H5O7). What are the masses of theproducts if there is 1.00 gram of each reactant in thetablet. Use the net ionic equation to solve thisproblem.What is the percent yield if only 1.25g of gas wasproduced? How does this affect the resulting mass ofyour other product?
Practice Problem #8sodium bicarbonate, and citric acid (H3C6H5O7).What are the masses of the products if there is 1.00gram of each reactant in the tablet.Use the net ionic equation to solve this problem.
Practice Problem #8What is the percent yield if only 1.25g of gas wasproduced? How does this affect the resulting mass ofyour other product?
Key Concepts Balanced chemical equations can be interpreted in terms of moles, mass, and representative particles (atoms, molecules, formula units). The law of conservation of mass applies to all chemical reactions. Mole ratios are derived from the coefficients of a balanced chemical equation. Each mole ratio relates the number of moles of one reactant or product to the number of moles of another reactant or product in the chemical reaction.
Key Concepts Chemists use stoichiometric calculations to predict the amounts of reactants used and products formed in specific reactions. The first step in solving stoichiometric problems is writing the balanced chemical equation. Mole ratios derived from the balanced chemical equation are used in stoichiometric calculations. Stoichiometric problems make use of mole ratios to convert between mass and moles.
Key Concepts The limiting reactant is the reactant that is completely consumed during a chemical reaction. Reactants that remain after the reaction stops are called excess reactants. To determine the limiting reactant, the actual mole ratio of the available reactants must be compared with the ratio of the reactants obtained from the coefficients in the balanced chemical equation. Stoichiometric calculations must be based on the limiting reactant.
Key Concepts The theoretical yield of a chemical reaction is the maximum amount of product that can be produced from a given amount of reactant. Theoretical yield is calculated from the balanced chemical equation. The actual yield is the amount of product produced. Actual yield must be obtained through experimentation
Key Concepts Percent yield is the ratio of actual yield to theoretical yield expressed as a percent. High percent yield is important in reducing the cost of every product produced through chemical processes.
QuestionsWhat law are all stoichiometric calculations based on?A. law of definite proportionsB. law of conservation of massC. law of conservation of energyD. none of the above
QuestionsThe mole ratios can be determined only if what?A. all the reactants are present in equal amountsB. the reactants do not have coefficientsC. the products do not have coefficientsD. the equation is balanced
QuestionsIf the following reaction yields 5 mol NaAu(CN)2, how many moles of Au were present as reactants? (Assume all other reactants are in excess). 4Au(s) + 8NaCN(aq) + O2 + 2H2O(l) → 4NaAu(CN)2(aq) + 4NaOH(aq)A. 1B. 4C. 5D. 20
QuestionsIn the following reaction, how many moles of NaCN are required to react with 5 mol of Au? 4Au(s) + 8NaCN(aq) + O2 + 2H2O(l) → 4NaAu(CN)2(aq) + 4NaOH(aq)A. 3B. 5C. 8D. 10
QuestionsIn the following reaction, what mass of NaOH is produced if 5.0 moles of NaAu are also produced in the reaction? 4Au(s) + 8NaCN(aq) + O2 + 2H2O(l) → 4NaAu(CN)2(aq) + 4NaOH(aq)A. 20 gB. 50 gC. 200 gD. 400 g
QuestionsThe SI base unit of amount is ____.A. the gramB. the kilogramC. the moleD. Avogadro’s number
QuestionsZinc reacts with iodine in a synthesis reaction: Zn + I2 Znl2. What is the theoretical yield of Znl2, if 1.912 mol of zinc is used?A. 6.103 gB. 61.03 gC. 610.3 gD. 0.6103 g
QuestionsIn a chemical reaction, the statement that matter is neither created nor destroyed is based on what?A. mole ratioB. law of conservation of massC. Avogadro’s numberD. law of definite proportions
QuestionsWhich is not a product that must be produced in a double replacement reaction?A. waterB. heatC. precipitatesD. gases
QuestionsThe ____ is the maximum amount of product that can be produced from a given amount of reactant.A. theoretical yieldB. actual yieldC. limiting reactantD. excess reactant