6Look at it differently 2H2 + O2 ® 2H2O 2 dozen molecules of hydrogen and 1 dozen molecules of oxygen form 2 dozen molecules of water.2 x (6.02 x 1023) molecules of hydrogen and 1 x (6.02 x 1023) molecules of oxygen form 2 x (6.02 x 1023) molecules of water.2 moles of hydrogen and 1 mole of oxygen form 2 moles of water.
7In terms of Moles 2 Al2O3 ® 4Al + 3O2 The coefficients tell us how many moles of each kind
8In terms of massThe law of conservation of mass appliesWe can check using moles2H2 + O2 ® 2H2O2.02 g H22 moles H2=4.04 g H21 moles H232.00 g O21 moles O2=32.00 g O21 moles O236.04 g reactants36.04 g reactants
9In terms of mass 2H2 + O2 ® 2H2O 2H2 + O2 ® 2H2O 18.02 g H2O 2 moles H2O=1 mole H2O2H2 + O2 ® 2H2O36.04 g (H2 + O2)=36.04 g H2O
10Your turnShow that the following equation follows the Law of conservation of mass.2 Al2O3 ® 4Al + 3O2
11Mole to mole conversions 2 Al2O3 ® 4Al + 3O2every time we use 2 moles of Al2O3 we make 3 moles of O22 moles Al2O33 mole O2or3 mole O22 moles Al2O3
12Mole to Mole conversions How many moles of O2 are produced when 3.34 moles of Al2O3 decompose?2 Al2O3 ® 4Al + 3O23.34 moles Al2O33 mole O2=5.01 moles O22 moles Al2O3
13Your Turn2C2H2 + 5 O2 ® 4CO2 + 2 H2OIf 3.84 moles of C2H2 are burned, how many moles of O2 are needed?How many moles of C2H2 are needed to produce 8.95 mole of H2O?If 2.47 moles of C2H2 are burned, how many moles of CO2 are formed?
14Mole to Mole Conversions 2C2H2 + 5 O2 ® 4CO2 + 2 H2OHow many moles of C2H2 are needed to produce 8.95 mole of H2O?If 2.47 moles of C2H2 are burned, how many moles of CO2 are formed?
15Mass in Chemical Reactions How much do you make?How much do you need?
16We can’t measure moles!! What can we do? We can convert grams to moles.Periodic TableThen use moles to change chemicalsBalanced equationThen turn the moles back to grams.Periodic table
17Periodic TableBalanced EquationPeriodic TableMass g AMolesAMolesBMass g BDecide where to start based on the units you are givenand stop based on what unit you are asked for
18Conversions 2C2H2 + 5 O2 ® 4CO2 + 2 H2O How many moles of C2H2 are needed to produce 8.95 g of H2O?If 2.47 moles of C2H2 are burned, how many g of CO2 are formed?
19For example...If 10.1 g of Fe are added to a solution of Copper (II) Sulfate, how much solid copper would form?Fe + CuSO4 ® Fe2(SO4)3 + Cu2Fe + 3CuSO4 ® Fe2(SO4)3 + 3Cu1 mol Fe63.55 g Cu10.1 g Fe3 mol Cu55.85 g Fe2 mol Fe1 mol Cu=17.3 g Cu
202Fe + 3CuSO4 ® Fe2(SO4)3 + 3Cu3 mol Cu0.272 mol Cu0.181 mol Fe=2 mol Fe63.55 g Cu0.272 mol Cu=17.3 g Cu1 mol Cu
21Could have done it 1 mol Fe 63.55 g Cu 10.1 g Fe 3 mol Cu 55.85 g Fe =17.3 g Cu
22More ExamplesTo make silicon for computer chips they use this reactionSiCl4 + 2Mg ® 2MgCl2 + SiHow many moles of Mg are needed to make 9.3 g of Si?3.74 mol of Mg would make how many moles of Si?How many grams of MgCl2 are produced along with 9.3 g of silicon?
23For Example The U. S. Space Shuttle boosters use this reaction 3 Al(s) + 3 NH4ClO4 ® Al2O3 + AlCl3 + 3 NO + 6H2OHow much Al must be used to react with 652 g of NH4ClO4 ?How much water is produced?How much AlCl3?
26We can also change Liters of a gas to moles At STP 0ºC and 1 atmosphere pressureAt STP 22.4 L of a gas = 1 moleIf 6.45 moles of water are decomposed, how many liters of oxygen will be produced at STP?
27For ExampleIf 6.45 grams of water are decomposed, how many liters of oxygen will be produced at STP?H2O ® H2 + O22H2O ® 2H2 + O21 mol H2O1 mol O222.4 L O26.45 g H2O18.02 g H2O2 mol H2O1 mol O2
28Your TurnHow many liters of CO2 at STP will be produced from the complete combustion of 23.2 g C4H10 ?What volume of oxygen will be required?
29ExampleHow many liters of CH4 at STP are required to completely react with 17.5 L of O2 ?CH4 + 2O2 ® CO2 + 2H2O22.4 L O21 mol O21 mol CH422.4 L CH41 mol O21 mol CH422.4 L CH417.5 L O222.4 L O22 mol O21 mol CH4= 8.75 L CH4
30Avagadro told usEqual volumes of gas, at the same temperature and pressure contain the same number of particles.Moles are numbers of particlesYou can treat reactions as if they happen liters at a time, as long as you keep the temperature and pressure the same.
31ExampleHow many liters of CO2 at STP are produced by completely burning L of CH4 ?CH4 + 2O2 ® CO2 + 2H2O1 L CO217.5 L CH4= 17.5 L CO21 L CH4
32Particles We can also change between particles and moles. 6.02 x 1023 MoleculesAtomsFormula units
33Limiting Reactants Available Ingredients 4 slices of bread 1 jar of peanut butter1/2 jar of jellyLimiting ReactantbreadExcess Reactantspeanut butter and jelly
34Limiting ReagentIf you are given one dozen loaves of bread, a gallon of mustard and three pieces of salami, how many salami sandwiches can you make?The limiting reagent is the reactant you run out of first.The excess reagent is the one you have left over.The limiting reagent determines how much product you can make
35Limiting Reactants Limiting Reactant used up in a reaction determines the amount of productExcess Reactantadded to ensure that the other reactant is completely used upcheaper & easier to recycle
36How do you find out? Do two stoichiometry problems. The one that makes the least product is the limiting reagent.For exampleCopper reacts with sulfur to form copper ( I ) sulfide. If 10.6 g of copper reacts with 3.83 g S how much product will be formed?
37If 10. 6 g of copper reacts with 3. 83 g S If 10.6 g of copper reacts with 3.83 g S. How many grams of product will be formed?2Cu + S ® Cu2SCu is Limiting Reagent1 mol Cu1 mol Cu2Sg Cu2S10.6 g Cu63.55g Cu2 mol Cu1 mol Cu2S= 13.3 g Cu2S= 13.3 g Cu2S1 mol S1 mol Cu2Sg Cu2S3.83 g S32.06g S1 mol S1 mol Cu2S= 19.0 g Cu2S
38How much excess reagent? Use the limiting reagent to find out how much excess reagent you usedSubtract that from the amount of excess you started with
39Your turn Mg(s) +2 HCl(g) ® MgCl2(s) +H2(g) If 10.1 mol of magnesium and 4.87 mol of HCl gas are reacted, how many moles of gas will be produced?How much excess reagent remains?
40Your Turn IIIf 10.3 g of aluminum are reacted with 51.7 g of CuSO4 how much copper will be produced?How much excess reagent will remain?
43Yield The amount of product made in a chemical reaction. There are three typesActual yield- what you get in the lab when the chemicals are mixedTheoretical yield- what the balanced equation tells you you should make.Percent yield = Actual x 100 % Theoretical
44Percent YieldWhen 45.8 g of K2CO3 react with excess HCl, 46.3 g of KCl are formed. Calculate the theoretical and % yields of KCl.K2CO3 + 2HCl 2KCl + H2O + CO2? g45.8 gactual: 46.3 g
45Percent Yield K2CO3 + 2HCl 2KCl + H2O + CO2 ? g 45.8 g actual: 46.3 gTheoretical Yield:45.8 gK2CO31 molK2CO3g2 molKCl1 molK2CO374.55g KCl1 molKCl= 49.4g KCl
46Percent Yield K2CO3 + 2HCl 2KCl + H2O + CO2 45.8 g 49.4 g actual: 46.3 gTheoretical Yield = 49.4 g KCl46.3 g49.4 g% Yield = 100 =93.7%
47Example6.78 g of copper is produced when 3.92 g of Al are reacted with excess copper (II) sulfate.2Al + 3 CuSO4 ® Al2(SO4)3 + 3CuWhat is the actual yield?What is the theoretical yield?What is the percent yield?If you had started with 9.73 g of Al, how much copper would you expect?
48Details Practice Percent yield tells us how “efficient” a reaction is. Percent yield can not be bigger than 100 %.How would you get good at this?Practice