Quantitative Analysis CHEM 3000
Weber State University
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Date Created: 10/28/15
Weber State University H CHEM 3000 Quantitative Analysis H Chemical Equilibrium Reading Sections Chapter 6 Only two options in nature in equilibrium or approaching equilibrium How a system achieves equilibrium and how long it takes are answered by chemical kinetics amp thermodynamics Kinetics Guldenberg amp Waage 1864 described the laW of mass action Which basically states that the rate of a Chemical reaction is proportional to the active masses concentration or pressure of the reacting species at any time At equilibrium the rate of the forward reaction equals the rate of the reverse reaction ratef rater ratef kfAaBb A EM rater krCCDd Energy Products 89 Reactants Reaction Progress Fast Slow large small kf Slow Fast small kr large k If kf gtgt kr If kfltlt kr A reaction is favored to form products when Rules of Thumb Large values of K gt103 Small values of K lt10393 Intermediate values of K 10393ltKlt103 Remember the equilibrium state is a The Equilibrium Constant CCDd aAbB cCdD A B K is a unitless quantity Why In the thermodynamic derivation of the equilibrium constant each quantity in the equilibrium constant expression is expressed as the ratio of the concentration of a species to its concentration in its standard state For solutes the standard state is 1 M For gases the standard state is 1 atm 1 bar latm 101 bar It is understood that the term A really means EA M1 pressure D in atm If D is a gas D really means 1 atm What if C is a pure liqugfi or solid The ratlo concentration of C in its standard state state E the pure l1qu1d or sol1d is equal to 1 because the standard Consider the following equilibria Agaq Cl aq e AgClaq K1220gtlt103 AgClaq Cl aq e AgClZ aq K2293gtlt101 AgCls e Agaq Cl aq K3l8gtlt10 10 Note All species in book are in aqueous solution unless otherwise stated Calculate the numerical value of the equilibrium constant for the reaction AgCls e AgClaq Agaq Cl aq e AgClaq A2C1S e A2ac C1 acl Calculate the concentration of AgClaq in equilibrium With excess undissolved solid AgCl Find the numerical value of K for the reaction AgClZ aq e AgCls Cl aq AgC1aq e Agaq C1 aq K AgC12 aq e AgClaq Cl aq K Agaq Cl aq e AgCls K Thermodynamics the area of chemistry that deals with the study of the interconversion transfer and dispersal of energy among its various forms g Reactants Concerned only with the initial and a nal states and does not require knowledge of the pathway w Reaction Progress gt AH Heat absorbed or lost from a system at constant pressure AS Measure of disorder or randomness of a system AG Energy available to do work Reactants 9 Products Reactions that have K gtgt 1 Reactants T Reactions that have K ltlt 1 W k G AG or Reactlons that have K 1 Products Reaction progress gt There must be a relationship then between AGIO and K IfKgt1AGr IszleAGrquot IfKlt1AGr A system at equilibrium subjected to a change that disturbs the system Will proceed back to equilibrium in such a way as to offset the change Le Chatelier s Principle aAbBeCCdD Free Energy G Q I Reaction Quotient Q The formation of tetra uoroethylene from its elements is highly exothermic 2F2 g 2Cs e F2CCF2 g heat If a mixture of F2 graphite and CZF4 is at equilibrium in a closed container Will the reaction proceed to the left or right if F2 is added Rare bacteria from the planet Te on eat CZF2 and make Te on for their cell walls Will the reaction proceed to the left or right if these bacteria are added Will the reaction proceed to the left or right if solid graphite is added Will the reaction proceed to the left or right if the container is crushed to 18 its original volume Does the equilibrium constant become larger or smaller if the container is heated Some additional names for equilibrium constants Solubility Product KSp Complex Formation Kf or 3 Acid Hydrolysis Ka Base Hydrolysis Kb Water Autoprotolysis KW The above constants are for very specific chemical equations Solubility Product Equilibrium constant for the reaction in Which a solid salt dissolves to give its constituent ions in solution The solubility is the maximum molar concentration of salt that has dissolved in a saturated solution solid present in equilibrium with the dissolved species Calculate the molar solubility of Ag4FeCN6 FM64342 in water What if I dissolve Ag4FeCN6s in 0040 M AgNO3aq Will the solid be more or less soluble Quantitatively If the FeCN64 was xed at l lgtlt10398 M What is the maximum Ag in solution in equilibrium With solid just as precipitation begins Precipitation reactions can be used to quantitatively remove ions from solution or to separate ions from each other What concentration of carbonate must be added to a 010 M Zn2 solution to precipitate 9990 of the Zn2 A solution contains 00500 M Ca2 and 00300 M Ag Can 9900 of either ion be precipitated by addition of sulfate Without precipitating the other metal ion Which ion will ppt rst Ca2 or Ag Removing 9900 of Ca2 reduces its concentration to 5OOgtltlO394 M What 804239 in solution will achieve this result Will this so42 ppt Ag 00300 M What Will be the Ca2 When AgZSO4 just begins to precipitate What 804239 in solution will achieve this result At this 804239 What is Ca2 Complex Formation Lewis Acid Lewis Base Lewis acid Lewis base adduct with a coordinate covalent bond Pb2 I39 PbI I is a ligand of Pb2 Other adducts form PbI339 and Pb14239 Pb12s lt2 Pb2aq 2139aq Ks10 79gtlt10399 Observation Pb12s dissolves as 139 is increased At high 1 Pb12s dissolves Pb2 I e PbI Pb2 21 e Pb12aq Pb2 31 e PbI3 Pb2 41 e Pb142 Ksp 1 b2139l2 31 l0gtlt102 32 14x103 33 113 83gtlt103 34 PM 3 0x104 Pb2l 1394 At low I solubility of Pb2 is governed by ppt Pb12s At high I the previous equations are driven to the right A note about equilibrium constants from tables They are not constant Values from from various sources may be different The value may have been determined by different methods or conditions These conditions may include different solution compositions In some cases the K value was determined as ionic concentrations are extrapolated to zero Pay attention to notes concerning the table of K values to which you refer If you need a K value use the one that most closely matches your experimental conditions The cumulative formation constant for SnC12aq in 10 M NaNO3 is 32 12 Find the concentration of SnC12aq for a solution in which the concentrations of Sn2 and C1 are both somehow xed at 020 M Given that KspZnOH2 30x103916 31 25x104 33 72gtlt1015 34 28x1015 calculate the concentrations of each Zn containing species in a solution saturated With ZnOH2s and containing OH at a xed concentration of 32x10 7 M ZnOH2s e Zn2 ZOH39 Zn2 OH39 9 ZnOH Zn2 30H39 9 ZnOH339 Zn2 40H39 9 ZnOH4239 AcidBase Equilibria Acid Substance that is a proton H donor or produces H H3O when dissolved in water HF HNO3aq HZO a Base Substance that is a proton H acceptor or produces OH39 when dissolved in water NH3 NH3 g HZO 9 Strong acids and bases ionized essentially 100 in aqueous solution Autoprotolysis of Water H20 H20 H3O OH39 KW H3OOH39 l0gtltlO 14 ZSOC H3O l0gtltlO 7 M OH39 l0gtltlO 7 M Hydronium Ion Concentration H301 pH OH 1 01 M pH 10gH3O 1 00000000000001 M 001 M 2 0000000000001 M 0001 M 3 000000000001 M 00001 M 4 00000000001 M 000001 M 5 0000000001 M 0000001 M 6 000000001 M 00000001 M 7 00000001 M 000000001 M 8 0000001 M 0000000001 M 9 000001 M 00000000001 M 10 00001 M 000000000001 M 11 0001 M 0000000000001 M 12 001 M 00000000000001 M 13 01 M Kw H30OH39 10ng 3910gOH39H30 1400 10gOH 10gH3O 1400 pOH pH Baking soda Lake Ontario Human urine Saliva pH 57 71 Tomato juice Average pH of rainfall Toronto February 1979 Apples Lemon juice Ammonia Milk of magnesia Seawater Human blood Theoretical quotpurequot rain pH 56 Most fish species die pH 45 50 Vinegar Most acidic rainfall recorded in US at Wheeling W Va Battery acid Acidic mine water Iron Mountain Calif Figure67 Note There is no such thing as pure water CO2 H20 9 HCO3 H CO2 can be remove by boiling water and storing in an air tight container AcidBase ionization reactions Acid dissociationBase hydrolysis HA H20Z e H3O A K A H301 a HA B H20 e BHOH39 KbOH IH Carboxylic acids i R C OH O O HBC g OH H20 rgc ii o H3O Ka18gtlt105 Small highlycharged metal cations 3 2 Al3 6 A1 I H H20 Al H OH H3O 1391 i H 6 H 5 Ka l4gtltlO395 Amin es R N R R H or organlc group CH33N H20 9 CH33NH OH Kb l6gtltlO3910 Salts of strong acidsbases Salts formed from the neutralization reactions between acids and bases HCl NaOH 9 H20 NaClaq NaClaq H20 9 Salts of weak acidsbases CH3COONaaq H20 9 CH33NHClaq H20 9 The Ka amp Kb relationship CH33N H20 9 CH33NH OH39 Kb CH33NH H20 9 CH33N H3O Ka Polyprotic acidsbases Ionization occurs in stepWise fashion H2C03 H20 9 HCO3 H30 Kal K W b2 K HCO3 H20 9 C032 H30 K W 212 Kbl
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