Chem 109 Final -- Study Guide
Chem 109 Final -- Study Guide Chem 109
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This 0 page Study Guide was uploaded by y-chen9 on Monday December 14, 2015. The Study Guide belongs to Chem 109 at University of Wisconsin - Madison taught by Ive Hermans in Fall 2015. Since its upload, it has received 224 views. For similar materials see Advanced General Chemistry in Chemistry at University of Wisconsin - Madison.
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Date Created: 12/14/15
Chemistry 109 Final Review By Yang Chen Professor Ive Hermans TA Hangjian Zhao Textbook Chemistry The Molecular Sciencequot Moore amp Stanitski 5e Chapter 1246 8 Chemical Equilibrium 124 The Meaning of the Equilibrium Constant 0 KC tells us extent of reaction at equilibrium and can be used to calculate how much product will be present at equilibrium 0 KC gt 1 product favored 0 KC lt 1 l reactant favored 0 KC 1 l signi cant amount of reactant and product 0 If a reaction has a large tendency to occur in one direction then the reverse reaction has little tendency to occurquot Moore amp Stanitski 541 125 Using Equilibrium Constants Q reaction quotient like KC but is the ratio of actual concentrations 0 Q gt KC product concentration relatively too high Reaction should shift to reactants 0 Q lt KC product concentration relatively too low Reaction should shift to products Q KC system at equilibrium 126 Shifting a Chemical Equilibrium Le Chatelier s Principle 0 Le Chatelier s Principle If a simple at equilibrium is disturbed the system will counteract that disturbance by shifting to establish a new equilibrium 0 Changing concentrations of reactants or products is a disturbance 0 Increase reactant l forward shift 0 Decrease reactant back shift 0 Increase product back shift 0 Decrease product forward shift 0 Changing volume can be a disturbance changing pressure is a disturbance in gasphase reactants 0 Pressure can be changed by keeping volume same but adding or removing one or more substances o A decrease in volume increases pressure and vice versa 0 Changing pressure by changing volume shifts an equilibrium only if the sum of the coef cients for gasphase reactants is different from the sum of the coef cients for gasphase productsquot Moore amp Stanitski 552 0 Volume can also be changed by adding solvent 0 quotFor an endothermic reaction an increase in temperature always means an increase in Kc an endothermic reaction becomes more productfavored at higher temperaturesquot Moore amp Stanitski 544 o quotFor an exothermic reaction an increase in temperature always means a decrease in Kc an exothermic reaction becomes less productfavored at higher temperaturesquot Moore amp Stanitski 544 128 Controlling Chemical Reactions The HaberBosch Process 0 See page 559 for equilibrium system generalizationsreview The HaberBosch Process Arti cial nitrogen xation process used to make ammonia today Chapter 16 711 Thermodynamics Directionaity of Chemical Reactions 16 7 Gibbs Free Energy Changes andl Equilibrium Constants Ko standard equilibrium constant KC but each concentration is divided by the standardstate concentration of 1 molL and each pressure is divided by the standardstate pressure of 1 bar 0 unitless K lt 1 l reactant favored AG gt 0 Kgt 1 product favored AG lt 0 Slope ArGo RT an Gas phase reaction 0 K0 Kp no units 0 K0 Kp e AGRT R 0008314 kJmol 168 Gibbs Free Energy Maximum Work andl Energy Resources 0 What does ArG represent 0 The max useful work that can be done by a product favored system on its surroundings at constant volume and pressure 0 The min work that must be done to cause a reactant favored reaction to happen 0 Significance of AG 0 Fuel is an energy resource When burned AG is released and can be used to do something useful 0 For a productfavored reaction AG lt 0 Max useful work that can be done by the reaction 0 For a reactant favored reaction AG gt 0 Min work needed to force reaction to occur Change Q vs K Response Addition of reactant Q lt K Shifts R Addition of product Q gt K Shifts L Removal of reactant Q gt K Shifts L Removal of product Q lt K Shifts R Coupled Reaction Energy from one process is supplied from another 0 Coupling reactantfavored processes with productfavored processes EX charging a battery 169 Gibbs Free Energy and Biological Systems Coupling reactions are naturally occurring in biological systems 0 Humans are a lowentropy system 0 Gibbs free energy is temporarily stored in small pockets 0 Metabolism chemical changes that occur as food nutrients gets processed 0 Foods are oxidized 0 Gibbs free E released from oxidization allows other reactions to occur 0 Exergonic A reaction that releases Gibbs free E o Endergonic A reaction that consumes Gibbs free E o Gibbs free E and Krebs CycleCitric Acid Cycle 0 Gibbs free E and photosynthesis 0 Photosynthesis is endergonic 0 See diagram on page 728 1610 Conservation of Gibbs Free Energy 0 Energy conservationquot conservation of useful EGibbs free E 1611 Thermodynamics and Kinetic Stability A substance is thermodynamically stable if it does not undergo productfavored reactions at its lowest energy level 0 Something that is kinetically stable has a high activation barrier that presents it from reacting quickly Chapter 14 all Acids and Bases 141 BranstedLo wry Acids and Bases BronstedLowry acids are H proton donors BronstedLowry bases are H proton acceptors Weak Does not ionize completely Ionization of weak acids is a reactantfavored process 0 ln aqueous solutions all BL acids react with water 0 According to BL water is a base when acid is present and is an acid when base is present Conjugate AcidBase Pair A pair of molecules or ions related to each other by the loss or gain of a single H 0 One member of a conjugate acidbase pair is always a reactant and the other is always a product they are never both products or both reactants Which is the base and which is acid can depend on the direction of the reaction 0 Strong acids are better H donors than weak acids Stronger acids have weaker conjugate bases and vice versa Stronger bases have weaker conjugate bases and vice versa 0 As acid strength decreases conjugate base strength increases 0 As base strength decrease conjugate acid strength increases 142 Carboxyic Acids andl Amines A acids have carboxylic acid functional group COOH Amines are weak bases 143 The Autoionization of Water Autoionization Process were water molecules react to produce aqueous Hand OH39 0 KW Equilibrium ionization constant for water 0 KW H3OOH39 10 x 103971O x 10 10 x 103914 25 Celcius Applies to pure water and all aqueous solutions If one concentration increases the other decreases If we know one concentration we can calculate the other Concentrations also indicate solution as acid neutral or basic 0 If both concentrations are equal solution is neutral 144 The pH Scale 0 Neutral pH 7 acidic pH lt 7 basic pH gt7 0 pH is de ned as the negative of the base 10 log of the hydronium ion conc 0 pH ogH30 pOH ogOH39 145 Ionization Constants 0f Acids andl Bases ln acidbase reaction stronger reactant acid and base more productfavored This is the opposite of equilibrium constant 0 Greater equilibrium constant of an acid s ionization stronger acid Acid Ionization Constant Expression Equilibrium constant expression but for acid ionization equation 0 Ka Kb 0 Strong acidbase strong electrolytes l acidbase ionization gt1 l productfavored at equilibrium Monoprotic acids Can donate single H Polyprotic Can donate more than one H per molecule 0 H2504 H2CO3 H3PO4 Think Why are some acidsbases weaker than other acidsbases 146 Molecular Structure and Acid Strength Binary Acids Acids that contain just hydrogen and one other element As H A bond energies decreases down a group and the bond weakens and binary acid strengths increase Oxoacids Acids in which the acidic hydrogen is bonded directly to oxygen in an H O bond 0 Strongest HNO3 HCLO4 H2504 Acid strength decreases with the decreasing electronegativity of Z 0 Z H O Z Ka increases by approximately 105 for each additional oxygen atom attached to Z Carboxylic Acids COOH Amino Acids Building blocks of proteins that have at least one acidic carboxylic acid group and at least one basic amine group Zwitterion Structure containing both a negative charge COO39 and a positive charge NH3 Acidic Oxide Oxide that dissolves in water to give an acidic solution Basic Oxide give a basic solution The greater the electronegativity of an element is and the higher its oxidation state in an oxide is the greater the acidity of the oxide isquot 147 Problem Solving Using Ka and Kb Important Relationships When starting with just reactants equilibrium can only be achieved when products are formed at the expense of reactants Chemical equilibrium equation for ionization of acidreaction of base with water acid ionizationbase ionization Magnitude of Ka Kb indicates how far the forward rxn occurs equilibrium Ka x Kb Iw o Inverse relationship as Kagets bigger Kb gets smaller and vice versa 0 Study Equations 148 AcidBase Reactions of Salts Strong acid strong base salt water 0 Strong acid strong base neutral acid 0 Weak acid strong base basic salt 0 This is a hydrolysis reaction 0 Strong acid weak base acidic salt 0 Weak acid weak base determined by relative strengths of conjugate base and conjugate acid formed 0 speci c Ka and Kb needed 0 Ka greater more acidic Kb greater more basic 149 Lewis Acids and Bases Lewis Acid Can accept a pair of electrons to form a new bond cations Lewis Base Can donate a pair of electrons to form a new bond anions o If there39s a war soldiers are recruited from the military base if there should be a bond electrons are extracted from the Lewis basequot 0 Coordinate Covalent Bond Shared pair of electrons where both electrons come from the same atom fonrdmme b i itil llhfrlii lt l l in It tili i ii ii liraquot mm o All metal cations are potential Lewis acids 0 Complex Ion Metal ion bonded to 1 Lewis bases by coordinate covalent bonds Amphoteric Describes a substance that can react as both base and acid 0 Ex AOH3 acts as a Lewis acid when dissolved in strong base and acts as a BronstedLowry base when dissolved in strong acid 0 How to determine which is Lewis acid and which is Lewis base in an equation 0 1 Look at reactants o 2 If reactants are cation and anion cation is Lewis acid and anion is Lewis Base o 3 If charges are not given draw outimagine structures which one will be the donator Which one will be the acceptor Oxides of nonmetals behave as acids 0 Carbon dioxide is a weak acid 141 0 Additional Applied AcidBase Chemistry Acidsbases in everyday life 0 Neutralizing Stomach Acidity l Antacids l Tums 0 Cooking 0 Household cleaners Chapter 1512 Additional Aqueous Equilibria 151 Buffer Solutions Buffer Solutions Maintains almost constant pH when limited amounts of acidbase are added 0 Buffer Chemical system that resists change in pH It does this because it has both a weak acid that can react with base and weak base that can react with acid They are usually made of a weak acid and its conjugate base or a weak base and its conjugate acid 0 In equal concentrations Helpful httpwwwchemguidecoukphysicaIacidbase eqiabuffershtml httpchemcollectiveorgactivitiestutoriaIsbu ffersbuffersS If Ka and concentration of conjugate acid and conjugate base are known the pH can be calculated in two ways 0 Solve Ka expression for H30 0 Use HendersonHasselbalch equation 24 conjugate baee H K I K 1e P g eenjugate aeid o o The pH range of a buffer is limited to about one pH unit above or below the pKa of the conjugate acidquot 559 0 quotWhen acid is added to buffer the acid reacts with the conjugate base of the buffer to form its conjugate acidquot 660 0 quotWhen base is added to buffer the base reacts with the conjugate acid of the buffer which is converted into its conjugate basequot 660 0 quotWhen acid or base is added to buffer the pH changes because of a change in the ratio conjugate baseconjugate acid Buffer Capacity Amount of acidbase added that doesn t 152 AcidBase Titrations Titration Method in which concentrations of an acid or base can be determined by slowly adding one solution called a titrant o The equivalence point all acidbase has been reactedtitrated 0 End point color change Titration curve Graph of pH as a function of the volume of titrant added Titration of a strong acid with a strong base produces a neutral salt with pH 7 0 weak acid and strong base pH at equivalence point greater than 7 due to hydrolysis of the basic anion formed by the titration strong acid and weak base pH at equivalence point is less than 7 Titration of a polyprotic acid with base 0 Polyprotic acids have more than one ionizable hydrogen They react in two steps one for each ionizable H 0 Therefore two evuivalence points 1 7al AcidBase Titrations 171 Redox Reactions Transfer of electrons What determines if a reaction involves oxidationreduction 0 Presence of strong oxidizing or reducing agents as reactants o A change in oxidation number of one or more elements 0 The presence of an uncombined element as a reactant or product Oxidizing agents are reduced gain electrons Reducing agents are oxidized lose electrons rue mis t11 1 l 1 39339 1 l l U 1 l l Cu Ag Nil 1 2 39 quotLg jllf o isi lm lj is 3 3 oxidation III I 1 HalfReactlons andquot Reduction Dxidati m l in 9 Til391quot 5 H Hf I Ari HalfReactions Show reactants products and electrons transferred for either an oxidation or a reduction Not both A half reaction is obtained by considering the change in oxidation states of individual substances involved in the redox reaction Zn gtZn2i2 2Hl2ez Hl2 Zn2H Zn2lHZ An overall equation can always be generated by writing oxidation and reduction halfreactions using coef cients to adjust the halfreaction equations so the number of electrons released by the oxidation equals the number gained by the reduction and then adding the two halfreactions to give the equation for the overall reactionquot 773 1 73 Voltaic Cells Redox reactions favor products Voltaic Cell Way to capture useful work as electrical work 0 Also called electrochemical cell 0 Each voltaic cell contains two halfcells Anode Halfcell where oxidation occurs Cathode HalfCell where reduction occurs Electrode Conducts electrical current e into or out of something quotElectrons move from the anode to the cathode through an external electrical circuitquot 746 The electrical circuit is complete in the solution by movement of ions into and out of a salt bridge which permits movement of anions and cations but prevents mixing of the anode and cathode solutionsquot 746 1 74 Voltaic Cells and Cell Potential Flow of e from anode to cathode difference in electrical potential E Electrical work electrical charge x potential energy difference Columb C Quantity of charge that passes a xed point in an electrical circuit when a current of 1 ampere ows for 1 secondquot 749 o Ampere A SI unit of electric current o 1 culomb 1 ampere x 1 second 0 Volt V Energy measured in J OneJ of work is performed when one coulomb of charge moves through a potential difference of one voltquot 749 0 Cell PotentialCell Voltage Electrical potential energy difference of a voltaic cell StandardState Conditions quotConditions where all reactants and products are present as pure solids pure liquids gases at 1 bar pressure or solutes at 1 M concentrationquot 750 o quotA very important point about halfcell potentials is that they apply to halfcells that is electrodes not to halfreactionsquot 750 1 75 Using Standard Halfcell Potentials Standard Halfcell Potential A halfcell potential measured under standard conditions by comparison with a standard hydrogen electrodequot 754 Halfcells below the hydrogen halfcell have a negative standard halfcell potential because when paired with a standard hydrogen electrodequot Table Standard Halfcell Potentials in Aqueous Solution at 25 C 0 See page 156 for important points about the table 0 The strength of oxidizing agents decreases as you move down the Table of Standard Reduction Potentials o The strength of reducing agents increases as you move down 176 E 0amp9 Gibbs Free Energy and K 0 o The sign of E Ceudetermines whether a reaction is product favored or reactantfavored 0 Positive E Cellis productfavored Faraday Constant 96485 x 10quot4 Cmol of electrons The electrical work that can be done by a cell is equal to the Faraday constant F multiplied by the number of electrons transferred in the overall reaction n and by the cell potential Eocelquot 0 Electrical work done by a cell nF E059 0 177 Effect of Concentration on Cell Potential The Nernst Equation Nernst Equation 0 RT Ecell E ElnKeq 0 I7 is the number of electrons transferred in the reaction from balanced reaction 0 F is the Faraday constant 96500 Cmol and 0 E is potential difference 0 Concentration Cell quotA voltaic cell that has the same chemical species in the anode and cathode compartments but with different concentrationsquot 763 0 pH meter Special conc cell that either has 2 electrodes Changing the concentrations or pressures of the reactants and products or changing the available energy in the system will take the system out of equilibrium The response to that change will be either a shift away from an increasing change or a shift toward a decreasing change Changing the amounts of solids or liquids will not affect the equilibrium position Increasing the volume decreases concentration The reaction shifts toward the products right Decreasing the temperature removes energy The reaction shifts toward the reactants left to evolve more energy
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