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2/17 Pre-AP YOUR TESTS HAVE NOT BEEN GRADED Pick up the paper from the side table Keep the mole packet you received yesterday. HAVE A SEAT IN THE SAME SEAT YOU WERE ASSIGNED YESTERDAY. You will need a blank piece of paper and something to write with. We will take a large portion of the class to write a FIVE PARAGRAPH paper over a writing prompt involving chemistry. This is a grade and must be done in ALL core classes. I need you to take it seriously. I time permits, we will start stoichiometry with the mole ratio (and the packet you received yesterday will make more sense to you) HW: Empirical Formula project 2/21 Pre-AP Pick up the papers from the side table HAVE A SEAT IN THE SAME SEAT YOU WERE ASSIGNED WHEN YOU TESTED. WE will start stoichiometry today with mole ratio and mole to mole calculations You will get your tests back on Thursday and we will discuss the results 4th period: you can use one of my calculators (AS LONG AS NONE GO MISSING FROM YOUR PERIOD. HW: MOLE RATIO WORKSHEETS (whatever we didn’t finish in class) Stoichiometry Introduction to Stoichiometry Ideal Stoichiometric Calculations Limiting Reactants & Percent Yield Introduction to Stoichiometry Reaction Stoichiometry Involves the mass relationships between reactants and products in a chemical reaction. 4 types of problems (given, unknown) Mole to mole Mole to mass Mass to mole Mass to mass Conversion Factors There are only 2 equalities that you will use to solve these problems!! Always start with a balanced chemical equation. From this, you can derive the mole ratio A conversion factor that relates the amounts in moles of any two substances involved in a chemical equation. Mole Ratio 2Al2O3(l) 4Al(s) + 3O2(g) We can write mole ratios that relate any two substances involved in the reaction. For example: 2 mol Al 2 O3 4 mol Al 3 mol O 2 2 mol Al 2 O3 4 mol Al 3 mol O 2 Which substances you use and which in on top/bottom is determined by what you are converting to/from. Molar Mass The other conversion factor you may use is the molar mass. Used to convert between moles and grams of the same substance. Numbers are off of the periodic table and rounded off at the hundredths position before use. Ex: Molar mass of Al2O3= 2(26.98 g/mol) + 3(16.00 g/mol)=101.96 g/mol Ideal Stoichiometric Calculations 4 types of problems Mole to mole Mole to mass Mass to mole Mass to mass General pathway: Mass given mole given mole unknown mass unknown Mole to mole Mass given mole given mole unknown mass unknown Given quantity is in moles Unknown quantity is in moles Need 1 conversion factor to solve Mole ratio to convert between mole given & mole unknown # mol given mol unknown x mol unknown 1 mol given Mole to mole example CO2(g) + 2LiOH(s) Li2CO3(s) + H2O(l) How many moles of lithium hydroxide are required to react with 20. mol of CO2? Given: 20. mol CO2 Unknown: ? mol LiOH 20. mol CO2 2 mol LiOH x 40. mol LiOH 1 1 mol CO 2 Mole to mole example The elements lithium and oxygen react explosively to form lithium oxide. How many moles of lithium oxide will form if 2 mole of lithium react with unlimited oxygen? Balanced eqn: 4Li + O2 2Li2O Answer: 1 mol Li2O Mole to mass Mass given mole given mole unknown mass unknown Given quantity is in moles Unknown quantity is mass (g, kg, etc.) Need 2 conversion factors to solve: Mole ratio to convert from mole given to mole unknown Molar mass to convert from mole unknown to mass unknown # mol given mol unknown mass unknown x x mass unknown 1 mol given 1 mol unknown Mole to mass example 6CO2(g) + 6H2O(l) C6H12O6(s) + 6O2(g) What mass, in grams, of glucose is produced when 3.00 mol of water react with carbon dioxide? Given: 3.00 mol water Unknown: ? grams glucose 3.00 mol H 2 O 1 mol C6 H12O 6 180.18 g C6 H12O 6 x x 90.1 g C6 H12O 6 1 6 mol H 2 O 1 mol C6 H12O 6 Mole to mass example 2NaN3(s) 2Na(s) + 3N2(g) If 0.500 mol of NaN3 react, what mass in grams of N2 would result? Given: 0.500 mol NaN3 Unknown: ? grams N2 Answer: 21.0 g N2 Mass to mole Mass given mole given mole unknown mass unknown Given quantity is a mass (g, kg, etc.) Unknown quantity is in moles Need 2 conversion factors to solve: Molar mass to convert from mass given to mole given Mole ratio to convert from mole given to mole unknown # g given 1 mol given mol unknown x x mol unknown 1 g given mol given Mass to mole example 4NH3(g) + 5O2(g) 4NO(g) + 6H2O(g) This reaction is run using 824 g NH3 & excess O2. How many moles of NO are formed? Given: 824 g NH3 Unknown: ? mol NO 824 g NH3 1 mol NH3 4 mol NO x x 48.4 mol NO 1 17.04 g NH3 4 mol NH3 Mass to mole example 4NH3(g) + 5O2(g) 4NO(g) + 6H2O(g) This reaction is run using 824 g NH3 & excess O2. How many moles of H2O are formed? Given: 824 g NH3 Unknown: ? mol H2O Answer: 72.6 mol H2O AP CHEM…. Take out a clean piece of paper Answer the following WITHOUT looking at Kinetics notes 1. Define Kinetics. 2. What needs to happen to reactant molecules in order for successful collisions to occur to increase the rate of a reaction? 3. List and EXPLAIN three factors that affect the rate of a reaction. 4. How much of a temperature increase will double the reaction rate? 5. Describe how a catalyst such as manganese oxide speeds up a reaction. AP Pick up the graded papers from the side table Leave your IMF test and Ch8/Ch9 Quiz out Turn in the Practice AP Test 3/17 WELCOME BACK! Pick up your graded papers or wait until someone passes them out. On the back of the stoichiometry quiz, answer the following: 1. 4NH3(g) + 5O2(g) 4NO(g) + 6H2O(g) This reaction is run using 824 g NH3 & excess O2. How many grams of NO are formed? 2. 2NaN3(s) 2Na(s) + 3N2(g) If 0.500 mol of NaN3 react, how many moles of N2 would result? 4NH3(g) + 5O2(g) 4NO(g) + 6H2O(g) This reaction is run using 824 g NH3 & excess O2. How many grams of NO are formed? 2NaN3(s) 2Na(s) + 3N2(g) If 0.500 mol of NaN3 react, how many moles of N2 would result? Today you will need… A calculator, a periodic table, the mass to mass worksheet you picked up Friday Take out the mole ratio WS and TURN IN IF COMPLETED If you didn’t finish, you have ten minutes Answer the following on a piece of paper: The elements lithium and oxygen react explosively to form lithium oxide. How many moles of lithium oxide will form if 2 mole of lithium react with unlimited oxygen? The elements lithium and oxygen react explosively to form lithium oxide. How many moles of lithium oxide will form if 2 mole of lithium react with unlimited oxygen? Mass to mass Mass given mole given mole unknown mass unknown Given quantity is a mass (g, kg, etc.) Unknown quantity is a mass Need 3 conversion factors to solve: Molar mass to convert from mass given to mole given Mole ratio to convert from mole given to mole unknown Molar mass to covert from mole unknown to mass unknown # g given 1 mol given mol unknown mass unknown x x x mass unknown 1 g given mol given 1 mol unknown Mass to mass example NH4NO3(s) N2O(g) + 2H2O(l) How many grams of NH4NO3 are required to produce 33.0 g N2O? Given: 33.0 g N2O Unknown: ? g NH4NO3 33.0 g N 2 O 1 mol N 2 O 1 mol NH 4 NO3 80.06 g NH 4 NO3 x x x 60.0 g NH 4 NO3 1 44.02 g N 2 O 1 mol N 2 O 1 mol NH 4 NO3 AP Take out Kinetics notes Mass to mass example What mass of aluminum is produced by the decomposition of 5.0 kg of Al2O3? Given: 5.0 kg Al2O3 Unknown: ? g Al Balanced eqn: 2Al2O3 4Al + 3O2 Answer: 2.6 kg Today you will need… The lab paper from the side table Pick up YOUR graded papers A calculator, a periodic table, something to write with Take out the mass to mass homework We will practice mole to mole and mass to mass problems today We will also prepare for the lab you have Wednesday/Thursday Add the following questions to your mass to mass HW from last night. These will count as 8, 9, 10 In a very violent reaction called a thermite reaction, aluminum metals reacts with iron(III) oxide to form iron metal and aluminum oxide according to the following equation: Fe2O3 + Al Fe + Al2O3. 8. What is the mole ratio of Al to Fe? Of aluminum oxide to iron (III) oxide? 9. What mass of Fe will be produced from 130. g of Fe2O3? 10. How many moles of Al will react with 2.58 moles of Fe2O3? Ideal conditions These problems tell us the amount of reactants or products under ideal conditions. All reactants are completely converted into products. Give the maximum yield we could expect, but this is rarely attained in the field because we don’t have ideal conditions. 4th/6th Need: Paper from table, calculator, something to write with On a clean piece of paper: Explain limiting reactant Explain excess reactant (this will be turned in) Limiting Reactants & Percent Yield Limiting & excess reactants Once one of the reactants is completely used up in a rxn, it doesn’t matter how much of the other reactant(s) you have. The reaction cannot continue. Limiting reactant: The reactant that limits the amounts of the other reactants that can combine and the amount of product that can form in a chemical reaction. Limiting & excess reactants Excess reactant(s) Substance(s) that are not completely used up an a rxn and do not limit the amount of product that can be formed. These are the reactants that are “left over” at the end of a rxn. Which is limiting? Excess? To decide which reactant is limiting in a rxn, use one of your givens to solve for the other. Then compare how much you have (given) to how much you need under ideal conditions (solved for). If you have more than you need, the 1st substance is limiting. If you have less than you need, the 2nd substance is limiting. Limiting reactant example CO(g) + 2H2(g) CH3OH If 500. mol of CO and 750. mol of H2 are present, which is the limiting reactant? Solve to determine how much H2 would be needed to completely react 500. mol CO. 500. mol CO 2 mol H 2 x 10 0 0 mol H 2 1 1 mol CO Do you have 1000 mol H2? No, you only have 750. mol. H2 is the limiting reactant. Limiting reactant example 3ZnCO3(s) + 2C6H8O7(aq) Zn3(C6H5O7)2(aq) + 3H2O(l) + 3CO2(g) If there is 1 mol of ZnCO3 & 1 mol of C6H8O7, which is the limiting reactant? Answer: 1 mol ZnCO3 could react with 0.67 mol C6H8O7, which is less than is available. ZnCO3 is limiting. Limiting reactant example Aspirin, C9H8O4, is synthesized by the rxn of salicylic acid, C7H6O3, with acetic anhydride, C4H6O3. 2C7H6O3 + C4H6O3 2C9H8O4 + H2O When 20.0g of C7H6O3 and 20.0g of C4H6O3 react, which is the limiting reactant? How many moles of the excess reactant are used when the rxn is complete? What mass in grams of aspirin is formed? C7H6O3, 0.0724 mol, 26.1 g Percent Yield Theoretical yield-maximum amount of product that can be produces from a given amount of reactant. This is what we calculate using ideal stoichiometric calculations. Actual yield-the measured amount of a product obtained from a rxn. Percent Yield Ratio of the actual yield to the theoretical yield, multiplied by 100. actual yield % yield x 100 theoretica l yield Percent Yield example C6H6(l) + Cl2(g) C6H5Cl(s) + HCl(g) When 36.8g C6H6 react with an excess of Cl2, the actual yield of C6H5Cl is 38.8g. What is the percent yield? Given: 36.8g C6H6, excess Cl2, actual yield=38.8g C6H5Cl Unknown: ? g C6H5Cl, percent yield 36.8 g C 6 H 6 1 mol N 2 O 1 mol C 6 H 5Cl 112.56 g C 6 H 5Cl x x x 53.0 g C6 H 5Cl 1 78.12 g C 6 H 6 1 mol C6 H 6 1 mol C 6 H 5Cl % yield 38.8 g C6 H 5Cl actual yield x 100 x 100 73.2% theoretica l yield 53.0 g C6 H 5Cl Percent Yield example Methanol can be produced through the rxn of CO and H2 in the presence of a catalyst. CO(g) 2H2(g) CH3OH(l) catalyst If 75.0 g of CO reacts to produce 68.4 g CH3OH, what is the percent yield? Answer: 79.7% Percent Yield example 2ZnS(s) + 3O2(g) 2ZnO(s) + 2SO2(g) If the typical yield is 86.78%, how much SO2 should be expected if 4897 g of ZnS are used? Theoretica l yield 4897 g ZnS 1 mol ZnS 2 mol SO 2 64.07 g SO 2 x x x 3219.278 g SO 2 1 97.46 g ZnS 2 mol ZnS 1 mol SO 2 actual yield (% yield)(the oretical yield) % yield x 100 actual yield theoretica l yield 100 (86.78)(32 19.278 g SO 2 ) actual yield 2794 g SO 2 100