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We cant measure moles!! What can we do? We can convert grams to moles. Periodic Table Then use moles to change chemicals Balanced equation Then turn the moles back to grams. Periodic table

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Periodic Table Moles A Moles B Mass g B Periodic Table Balanced Equation Mass g A Decide where to start based on the units you are given and stop based on what unit you are asked for

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Reaction 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 O 2 are produced by decomposing g of KClO 3 ? 2 KClO 3 (s) 2 KCl (s) + 3 O 2 (g) g149.2 g96 g 123.0xy use proportionality to get x = 74.8 g KCl; y = 48.2 g O 2

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Stoichiometry Calculations g KClO 3 How much KCl and O 2 are produced by decomposing g of KClO 3 ? 2 KClO 3 (s) 2 KCl (s) + 3 O 2 (g) g149.2 g96 g 123.0xy use proportionality to get x = 74.8 g KCl; y = 48.2 g O g O g KClO 3 1 mol O g O L O 2 1 mol O 2 Versatile, getting the amount in various units. Find amount of KCl in g, mol, and volume (specific gravity = 1.984) g KClO 3

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The Steps in a Stoichiometric Calculation Mass of substance A Moles of substance A Moles of substance B Mass of substance B Use molar mass of A Use molar mass of B Use coefficients of A & B in balanced eqn

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Conversions 2C 2 H O 2 4CO H 2 O How many moles of C 2 H 2 are needed to produce 8.95 g of H 2 O? If 2.47 moles of C 2 H 2 are burned, how many g of CO 2 are formed?

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For example... If 10.1 g of Fe are added to a solution of Copper (II) Sulfate, how much solid copper would form? Fe + CuSO 4 Fe 2 (SO 4 ) 3 + Cu 2Fe + 3CuSO 4 Fe 2 (SO 4 ) 3 + 3Cu 10.1 g Fe g Fe 1 mol Fe 2 mol Fe 3 mol Cu 1 mol Cu g Cu =17.3 g Cu

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2Fe + 3CuSO 4 Fe 2 (SO 4 ) 3 + 3Cu mol Fe 2 mol Fe 3 mol Cu = mol Cu 1 mol Cu g Cu =17.3 g Cu

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Could have done it 10.1 g Fe g Fe 1 mol Fe 2 mol Fe 3 mol Cu 1 mol Cu g Cu =17.3 g Cu

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More Examples To make silicon for computer chips they use this reaction SiCl 4 + 2Mg 2MgCl 2 + Si How 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 MgCl 2 are produced along with 9.3 g of silicon?

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For Example The U. S. Space Shuttle boosters use this reaction 3 Al(s) + 3 NH 4 ClO 4 Al 2 O 3 + AlCl NO + 6H 2 O How much Al must be used to react with 652 g of NH 4 ClO 4 ? How much water is produced? How much AlCl 3 ?

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Example Calculate the mass of sulfur dioxide (SO 2 ) produced when 3.84 mol O 2 is reacted with FeS 2 according to the equation: 4FeS O 2 2Fe 2 O 3 + 8SO mol m = ? 2.79 mol

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Another Example One of the most spectacular reactions of aluminium, the thermite reaction, is with iron oxide, Fe 2 O 3, by which metallic iron is made.

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The equation is : 2Al(s) + Fe 2 O 3 (s) Al 2 O 3 (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 Fe 2 O 3 that must be used for the operation? Calculate also how many grams of aluminium are needed. Strategy:

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2Al(s) + Fe 2 O 3 (s) Al 2 O 3 (s) + 2Fe(l) mass of Fe mol of Fe mol of Fe 2 O 3 mass of Fe 2 O 3

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Examples One way of producing O 2 (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 O 2 (g) are produced? How many grams of potassium chloride? How many grams of oxygen?

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Examples A piece of aluminum foil 5.11 in x 3.23 in x in is dissolved in excess HCl(aq). How many grams of H 2 (g) are produced? How many grams of each reactant are needed to produce 15 grams of iron form the following reaction? Fe 2 O 3 (s) + Al(s) Fe(s) + Al 2 O 3 (s)

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Examples K 2 PtCl 4 (aq) + NH 3 (aq) Pt(NH 3 ) 2 Cl 2 (s)+ KCl(aq) what mass of Pt(NH 3 ) 2 Cl 2 can be produced from 65 g of K 2 PtCl 4 ? How much KCl will be produced? How much from 65 grams of NH 3 ?

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How do you get good at this?

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Gases and Reactions

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We can also change Liters of a gas to moles At STP 0ºC and 1 atmosphere pressure At STP 22.4 L of a gas = 1 mole If 6.45 moles of water are decomposed, how many liters of oxygen will be produced at STP?

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For Example If 6.45 grams of water are decomposed, how many liters of oxygen will be produced at STP? H 2 O H 2 + O 2 2H 2 O 2H 2 + O g H 2 O g H 2 O 1 mol H 2 O 2 mol H 2 O 1 mol O L O 2

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Your Turn How many liters of CO 2 at STP will be produced from the complete combustion of 23.2 g C 4 H 10 ? What volume of oxygen will be required?

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Example How many liters of CH 4 at STP are required to completely react with 17.5 L of O 2 ? CH 4 + 2O 2 CO 2 + 2H 2 O 17.5 L O2O L O2O2 1 mol O2O2 2 O2O2 1 CH 4 1 mol CH L CH 4 = 8.75 L CH L O 2 1 mol O 2 1 mol CH L CH 4

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Avagadro told us Equal volumes of gas, at the same temperature and pressure contain the same number of particles. Moles are numbers of particles You can treat reactions as if they happen liters at a time, as long as you keep the temperature and pressure the same.

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Example How many liters of CO 2 at STP are produced by completely burning 17.5 L of CH 4 ? CH 4 + 2O 2 CO 2 + 2H 2 O 17.5 L CH 4 1 L CH 4 1 L CO 2 = 17.5 L CO 2

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Avogadros Principle of Gas Volumes: 9.2 #4 For balanced chemical eqns: 1 (mol) H + 1 (mol) Cl => 1 (mol) HCl (or volume) + (or volume) => 1 (or volume) HCl 2 (mol) H + 1 (mol) O => 1 (mol) H 2 O What if: 1 volume contained 1 mol of H? How many volumes of O needed for balanced rxn? How many volumes of H 2 O produced?

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Significance of this Relationship 9.2 #5 2 H (g) + 1 O (g) => 1 H 2 O (g) 2 atoms1 atom1 molecule 2 moles1 moles1 mole ** 2 volumes1 volume1 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.

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The Ideal Gas Law 9.3 #1 P V = n R T Use to describe some aspect of a gas under any single set of conditions Calculate moles, density or MW w this formula which is not limited 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)

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Ideal Gases 9.3 #2 Gases where each molecule in the gas sample is completely independent of one other: –molecules occupy no space (point masses) – No intermolecular interactions –Collisions completely elastic (no E lost) Ideal gases obey PV = nRT No real gas is truly ideal; but, most gases obey IGL Expect sig. dev. w conditions that allow high intermolecular interactions (highly conc., low T, polar molecules).

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Examples #1 What P is exerted by 1.8 mol N 2 in a 5.2 L vessel at 65 ˚C? 5.12 g of H 2(g) exerts 4.1 atm P in a 2.0 L vessel. Find T. What is the density of H 2(g) if a L sample exerts 3.5 atm of P at 200 K? Answers: 9.6 atm ; 38 K ; mol H 2 (0.213 g; 0.43 g/L)

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Example- Try at home #2 Gas 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. a.What is the product of the reaction? (100% yield) b.How many moles of product are produced? c.How many moles of B were reacted? d.What would the P of the product be in a 10 L vessel at 250 K? Answers: a) AB 2 b) 0.23 mol c) 0.46 mol d) 0.47 atm

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Example Stoich. Relationships 9.4 #3 Assume constant T and P. How many L of O 2(g) are needed to completely react with 14.0 L of C 4 H 10 ? 2 C 4 H 10(g) + 13 O 2(g) => 8 CO 2(g) + 10 H 2 O (l) The label on a gas cylinder is obscured. It could be Ne or N 2. The gas (2.50 g) occupies 2.00 L at 1.00 atm and 273 K. What is the gas?

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Solutions PV=nRT n = (PV)/(RT)n = mol gas Problem states gas sample is 2.50 g. MW = g / mol = 2.50 g/ mol = 28.2 g/mol = N 2(g) Constant T and P, so equal volumes contain equal moles. 2 C 4 H 10(g) + 13 O 2(g) => 8 CO 2(g) + 10 H 2 O (l) 14.0 L of C 4 H 10 x (13L O 2 /2 L C 4 H 10 ) = 91 L O 2(g)

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Example Stoich. Relationships 9.4 #4 a.A sample of H 2(g) occupies 5.00 L at STP. How many grams of H 2(g) are present? b.A sample of Cl 2(g) occupies 10.0 L at 4 atm at 273 K. How many L of Cl 2(g) are needed for a reaction with H 2(g) using: H 2(g) + Cl 2(g) => 2 HCl(g) Answer: a) 0.22 mol=0.44g ; b) 10 L at 4 atm, 273 K

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Real 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 dont exert as much pressure on container, and if the T is low or conc. high occupied volume significant and interactions incr. (P + n 2 a/V 2 ) (V-nb) = nRT a & b terms specific to each gas (can look up in tables) Corrected P Corrected V

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Solution Stoichiometry

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Solutions and Concentrations Concentrations 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. Explain solvent, solute, solution, and mixture For quantities in reactions: Amount = concentration * volume C 1 V 1 = C 2 V 2

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