Presentation on theme: "We can’t measure moles!! What can we do?"— Presentation transcript:
1We 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
2Periodic 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
3Reaction Stoichiometry Stoichiometry: quantitative relationship among reactants and products in a balanced reaction equation. Quantities may be in mole, mass, weight, or volume.How much KCl and O2 are produced by decomposing g of KClO3?2 KClO3(s) 2 KCl (s) + 3 O2 (g)245.2 g g 96 g x y use proportionality to get x = 74.8 g KCl; y = 48.2 g O2
4Stoichiometry Calculations How much KCl and O2 are produced by decomposing g of KClO3?2 KClO3(s) 2 KCl (s) + 3 O2 (g)245.2 g g 96 g x y use proportionality to get x = 74.8 g KCl; y = 48.2 g O2123.0 g KClO396.0 g O g KClO31 mol O g O222.4 L O2 1 mol O2123.0 g KClO3Versatile , getting the amount in various units.Find amount of KCl in g, mol, and volume (specific gravity = 1.984)
5The Steps in a Stoichiometric Calculation Mass of substance AUse molar mass of AMoles of substance AUse coefficients of A & B in balanced eqnMoles of substance BUse molar mass of BMass of substance B
6Conversions 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?
7For 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
82Fe + 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
9Could 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
10More 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?
11For 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?
12ExampleNot in Book!Calculate the mass of sulfur dioxide (SO2) produced when 3.84 mol O2 is reacted with FeS2 according to the equation:4FeS2 + 11O2 2Fe2O3 + 8SO23.84 molm = ?2.79 mol
13Not in Book! Another Example One of the most spectacular reactions of aluminium, the thermite reaction, is with iron oxide, Fe2O3, by which metallic iron is made.
142Al(s) + Fe2O3(s) Al2O3(s) + 2Fe(l) The equation is :2Al(s) + Fe2O3(s) Al2O3(s) + 2Fe(l)A certain welding operation, requires that at least 86.0 g of Fe be produced. What is the minimum mass in grams of Fe2O3 that must be used for the operation?Calculate also how many grams of aluminium are needed.Strategy:
152Al(s) + Fe2O3(s) Al2O3(s) + 2Fe(l) mass of Femol of Femol of Femol of Fe2O3mol of Fe2O3mass of Fe2O3
16ExamplesOne way of producing O2(g) involves the decomposition of potassium chlorate into potassium chloride and oxygen gas. A 25.5 g sample of Potassium chlorate is decomposed. How many moles of O2(g) are produced?How many grams of potassium chloride?How many grams of oxygen?
17ExamplesA piece of aluminum foil 5.11 in x 3.23 in x in is dissolved in excess HCl(aq). How many grams of H2(g) are produced?How many grams of each reactant are needed to produce 15 grams of iron form the following reaction? Fe2O3(s) + Al(s) ® Fe(s) + Al2O3(s)
18Examples K2PtCl4(aq) + NH3(aq) ® Pt(NH3)2Cl2 (s)+ KCl(aq) what mass of Pt(NH3)2Cl2 can be produced from 65 g of K2PtCl4 ?How much KCl will be produced?How much from 65 grams of NH3?
21We 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?
22For 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
23Your 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?
24ExampleHow 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
25Avagadro 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.
26ExampleHow 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
27Avogadro’s Principle of Gas Volumes: 9.2 #4 For balanced chemical eqns:1 (mol) H (mol) Cl => 1 (mol) HCl(or volume) + (or volume) => 1 (or volume) HCl2 (mol) H (mol) O => 1 (mol) H2OWhat if: 1 “volume” contained 1 mol of H? How many “volumes” of O needed for balanced rxn?How many volumes of H2O produced?
28Significance of this Relationship 9.2 #5 2 H(g) O(g) => H2O(g)2 atoms 1 atom 1 molecule2 moles 1 moles 1 mole** 2 “volumes” 1 volume 1 volume**A “volume” stoichiometry! This kind of stoichiometry holds just like mole stoichiometry, IFF all gaseous reactants and products are at the same T and P.
29The Ideal Gas Law 9.3 #1 P V = n R T •Use to describe some aspect of a gas under any singleset of conditions•Calculate moles, density or MW w this formula which is notlimited to std state conditions•Restrictions: applies to “Ideal Gas” and must use:P in atm V in L T in K (R= L-atm/mol K)
30Ideal Gases #2Gases where each molecule in the gas sample is completely independent of one other:molecules occupy no space (point masses)No intermolecular interactionsCollisions completely elastic (no E lost)Ideal gases obey PV = nRTNo real gas is truly ideal; but, most gases obey IGLExpect sig. dev. w conditions that allow high intermolecular interactions (highly conc., low T, polar molecules).
31Examples #1What P is exerted by 1.8 mol N2 in a 5.2 L vessel at 65 ˚C?5.12 g of H2(g) exerts 4.1 atm P in a 2.0 L vessel. Find T.What is the density of H2(g) if a L sample exerts 3.5 atm of P at 200 K?Answers: 9.6 atm ; 38 K ; mol H2 (0.213 g; 0.43 g/L)
32Example- Try at home #2Gas A (1 L) is mixed with gas B (2 L) both at the same T. A and B react quantitatively to produce 1 L of product at T. The 1 L product occupies 5.7 L at STP.What is the product of the reaction? (100% yield)How many moles of product are produced?How many moles of B were reacted?What would the P of the product be in a 10 L vessel at 250 K?Answers: a) AB2 b) 0.23 mol c) 0.46 mol d) 0.47 atm
33Example Stoich. Relationships 9.4 #3 Assume constant T and P. How many L of O2(g) are needed to completely react with 14.0 L of C4H10?2 C4H10(g) O2(g) => 8 CO2(g) H2O(l)The label on a gas cylinder is obscured. It could be Ne or N2. The gas (2.50 g) occupies 2.00 L at 1.00 atm and 273 K. What is the gas?
34Solutions Constant T and P, so ‘equal volumes’ contain ‘equal moles’. 2 C4H10(g) O2(g) => 8 CO2(g) H2O(l)14.0 L of C4H10 x (13L O2/2 L C4H10) = 91 L O2(g)PV=nRT n = (PV)/(RT) n = mol gasProblem states gas sample is 2.50 g.MW = g / mol = 2.50 g/ mol = 28.2 g/mol = N2(g)
35Example Stoich. Relationships 9.4 #4 A sample of H2(g) occupies 5.00 L at STP.How many grams of H2(g) are present?A sample of Cl2(g) occupies 10.0 L at 4 atm at 273 K. How many L of Cl2(g) are needed for a reaction with H2(g) using: H2(g) + Cl2(g) => 2 HCl(g)Answer: a) mol=0.44g ; b) 10 L at 4 atm, 273 K
36Real Gases and Ideal Gas Law 9.8 Real gases not ideal but deviations usually small.Van der Waals equation adjusts for ‘sticky force’ interactions and volume occupied by the gas.-if molecules attracted to each other they don’t exert as much pressure on container, and if the T is low or conc. high occupied volume significant and interactions incr.(P + n2a/V2) (V-nb) = nRTa & b terms specific to each gas(can look up in tables)Corrected PCorrected V
38Solutions and Concentrations Explain solvent, solute, solution, and mixtureConcentrations are expressed in many ways, g / 100 mL, g / L, mol / L (= M), mole fraction, weight fraction, percentage etc.Molarity is the expression of concentration in mole per liter.For quantities in reactions:Amount = concentration * volumeC1 V1 = C2 V2