capters 14-16 study guide
capters 14-16 study guide Chem 0120
Popular in General Chemistry 2
Popular in Chemistry
One Day of Notes
verified elite notetaker
This 22 page Study Guide was uploaded by Anna Perry on Thursday February 12, 2015. The Study Guide belongs to Chem 0120 at University of Pittsburgh taught by Dr. Vines in Winter2015. Since its upload, it has received 91 views. For similar materials see General Chemistry 2 in Chemistry at University of Pittsburgh.
Reviews for capters 14-16 study guide
Report this Material
What is Karma?
Karma is the currency of StudySoup.
You can buy or earn more Karma at anytime and redeem it for class notes, study guides, flashcards, and more!
Date Created: 02/12/15
Chapter 14 Chemical Equilibrium 141 Chemical Equilibrium A Dynamic Equilibrium a De ne dynamic equilibrium and chemical equilibrium Dynamic equilibrium An equilibrium in which molecular processes are continuously occurring Chemical equilibrium The state reached by a reaction mixture when the rates of forward and reverse reactions have become equal b Apply Stoichiometry to an equilibrium mixture Carbon monoxide and hydrogen react according to the following equann COg 3H2g gt CH4g H20g When 1000 mol CO and 3000 mol H2 are placed in a 1000L vessel at 927 C 1200K and come to equilibrium the mixture contains 0387 mol H20 What is the molar composition of the equilibrium mixture How many moles of each substance are present 142 The Equilibrium Constant Write equilibrium constant expressions The equilibrium constant expression for a reaction is an expression obtained by multiplying the concentrations of products dividing by the concentrations of reactants and raising each concentration term to a power equal to the coef cient in the chemical equation aA bB gt cC dD lC Dlquot C Kc Obtain an equilibrium constant from reaction composition The equilibrium constant Kc is the value obtained for the equilibriumconstant expression when equilibrium concentrations are substituted 0 What is the equilibrium constant for N2 3H2 gt 2NH3 Describe the equilibrium constant Kp indicate how Kp and Kc are related The equilibrium constant Kp is the equilibrium constant for a gaseous reaction in terms of partial pressures COW 3H2g gt CH4g H20g PHZ PCH4PH20 P 6 Also szKCRTA An the sum of the coefficients of products the sum of the coefficients of reactants R 008206 gt Clz If Kc 326 x 10392 at 191 C what is Kp Obtain Kc for a reaction that can be written as a sum of other reactions of known Kc values If a given chemical equation can be obtained by taking the sum of the other equations the equilibrium constant for the given equation equals the product of the equilibrium constants of the added equation A gt ZB K1 B2A 28 gt 3C K2 lCl3lBlZ A gt K3 K1K2 Reversed reaction Take the inverse N2 3H2 gt KCf X 2NH3gt N2 3H2 Kcr ch39l 23 x 10393391 443 Different moles N2 3H2 gt 2NH3 Kc 23 x 10393 12 N2 gt NH3 KC X 143 Heterogeneous Equilibria Solvents in Homogeneous Equilibria De ne homogeneous equilibrium and heterogeneous equilibrium Homogeneous equilibrium An equilibrium that involves reactants and products in a single phase Heterogeneous equilibrium An equilibrium involving reactants and products in more than one phase Write Kc for a reaction with pure solids or liquids In writing the Kc for a heterogeneous equilibrium you omit concentration terms for pure solids and liquids 3Fes 4H20g gt Fe3O4s 4H2g H20 Concentrations of Fe and Fe3O4 are omitted because the concentrations of a pure solid or liquid are constant at a given temperature 144 Qualitatively Interpreting the Equilibrium Constant Give a qualitative interpretation of the equilibrium constant based on its value By looking at the magnitude of Kc you can tell whether an equilibrium favors products or reactants If Kc gt 1 the mixture is mostly products If Kc lt 1 the mixture is mostly reactants If Kc z 1 the mixture contains appreciable amounts of both 145 Predicting the Direction of Reaction De ne reaction quotient Q The reaction quotient O is an expression that has the same form as the equilibriumconstant expression but whose concentration values are not necessarily those at equilibrium Describe the direction of reaction after comparing Q with If Qc gt Kc the reaction will go to the left If Qc lt Kc the reaction will go to the right If Qc z Kc the reaction mixture is at equilibrium c Use the reaction quotient A 500L reaction vessel contains 100 mol N2 300 mol H2 and 500 mol NH3 Wi more ammonia be formed or will it decompose when the mixture goes to equilibrium 0 Kc is 5 at 400 C 146 Calculating Equilibrium Concentrations a Obtain one equilibrium concentration give the others 0 A gaseous mixture contains 030 mol CO 010 mol H2 and 0020 mol H20 plus an unknown amount of CH4 in each liter This mixture is at equilibrium at 1200 K o What is CH4 Kc 392 b Solve an equilibrium problem involving a linear equation in x o If you start with 100 mol each of CO and H20 in a 500L vessel how many moles of each substance are in the equilibrium mixture at 1000 C 0 Kc 058 C Solve an equilibrium problem involving a quadratic equation in x 147 a c alter lf 100 mol H2 and 200 mol l2 are placed in a 100L vessel how many moles of each substance are in the gaseous mixture when it comes to equilibrium at 458 C Kc 497 Removing Products or Adding Reactants State Le Chatelier s principle Le Chatelier s principle states that when a system in chemical equilibrium is disturbed by a change of temperature pressure or concentration the system shifts in equilibrium composition in a way that tends to counteract this change of variable State what happens to an equilibrium when a reactant or product is added or removed When more reactant is added or some product is removed the net reaction occurs left to right in the forward direction to give a new equilibrium and more products are produced When more product is added or some reactant is removed the net reaction occurs right to left in the reverse direction to give a new equilibrium and more reactants are produced Apply Le Chatelier39s principle when a concentration is ed 0 Predict the direction of reaction when H2 is removed from a mixture lowering its concentration in which Hzlg Izlg gt 2Hllg 148 Changing the Pressure and Temperature a Describe the effect of a pressure change on chemical equilibrium If the pressure is increased by decreasing the volume of a reaction mixture the reaction shifts in the direction of fewer moles of gas b Apply Le Chatelier39s principle when the pressure is altered Decide whether an increase of pressure obtained by decreasing volume will increase decrease or have no effect on the amount of products COg C2g gt COC2g 2stg gt 2H2g 529 Cs 529 gt C52g c Describe the effect of a temperature change on chemical equilibrium For an endothermic reaction AH positive the amounts of products are increased at equilibrium by an increase in temperature Kc is larger at higher T For an exothermic reaction AH negative the amounts of products are increased by a decrease in temperature Kc is larger at lower T cl Apply Le Chatelier39s principle when the temperature is altered C02g Cs gt 2COg AH 1725 k o Is a high or low temperature more favorable to the formation of CO e Describe how the optimum conditions for a reaction are chosen 0 Consider the reaction 2C02g gt 2COg 029 AH 566 k 0 What temperature and pressure conditions would give the best yield of CO 149 Effect of a Catalyst De ne catalyst A catalyst is a substance that increases the rate of a reaction but is not consumed by it Compare the effect of a catalyst on rate of reaction with its effect on equilibrium A catalyst has no effect on the equilibrium composition of a reaction mixture it merely speeds up the attainment of equilibrium Describe how a catalyst can affect the product formed Although a catalyst can t affect the composition at true equilibrium in some cases it can affect the product in a reaction because it affects the rate of one reaction out of several possible reactions Extra Chapter 15 Acid Base Concepts 151 Arrhenius Concept of Acids and Bases De ne acid and base according to the Arrhenius concept An Arrhenius acid is a substance that when dissolved in water increases the concentration of hydronium ion H3O EX H20 gt H30 An Arrhenius base is a substance that when dissolved in water increases the concentration of hydroxide ion OH39 Ex NaOH H20 gt Na OH39 STRONG ACIDS HCO4 H2504 HI HBr HCI HNO3 STRONG BASES LiOH NaOH KOH CaOH2 SFOH2 BaOH2 152 BronstedLowry Concept of Acids and Bases a De ne acid and base according to the BronstedLowry concept A BronstedLowry acid is the species donating a proton in a protontransfer reaction A BronstedLowry base is the species accepting the proton in a protontransfer reaction b De ne the term conjugate acidbase pair A conjugate acidbase pair consists of two species in an acid base reaction one acid and one base that differ by the loss or gain of a proton The acid in such a pair is the conjugate acid of the base whereas the base is the conjugate base of the acid c Identify acid and base species 0 Label each species as an acid or base and show conjugate pairs HCO339aq HFaq gt H2CO3aq F39aq HCO339aq OH39aq gt CO3239aq H20 d De ne amphiprotic species An amphiprotic species is a species that can act as either an acid or base it can gain or lose an electron Ex HC0339 quotquotquot 153 Lewis Concept of Acids and Bases De ne Lewis acid and Lewis base A Lewis acid is a species that can form a covalent bond by accepting an electron pair from another species A Lewis base is a species that can form a covalent bond by donating an electron pair to another species Identify Lewis acid and Lewis base species 0 BOH3 H20 gt BOH439 H 154 Relative Strengths of Acids and Bases Understand the relationship between the strength of an acid and that of its conjugate base A strong acid loses its proton readily more readily than the weaker acid The strongest acids have the weakest conjugate bases and the strongest bases have the weakest conjugate acids Decide whether reactants or products are favored in an acidbase reaction An acidbase reaction normally goes in the direction of the weaker acid and base 0 Decide which direction the equation goes in SO42 gt 155 Molecular Structure and Acid Strength Note the two factors that determine relative acid strengths 1 The polarity of the bond to which the H atom is attached The more polarized the bond the more easily the proton is removed and the greater the acid strength 2 The strength of the bond HX Depends on size of atom X The larger atom X the weaker the bond and the greater the acid strength b Understand the periodic trends in the strengths of binary acids HX In going down a column of elements the size of atom X increases the HX bond strength decreases and the strength of the acid increases HFlt HClt HBrltH Going across a row of elements the electronegativity increases the HX bond polarity increases and the acid strength increases H2O lt c Understand the rules for determining the relative strengths of oxoacids HOY For a series of oxoacids of the same structure differing only in the atom Y the acid strength increases with the electronegativity of Y HIO lt HBrO lt HCIO For a series of oxoacids HOmYOn the acid strength increases with n the number of O atoms bonded to Y excluding O atoms in OH groups lt lt lt d Understand the relative acid strengths of a polyprotic acid and its anions The acid strength of a polyprotic acid and its anions decreases with increasing negative charge H2504 is a polyprotic acid that ionizes by losing a proton to give HSO439 which in turn ionizes to give 504239 HSO439 can lose a proton so it is acidic However because of the negative charge of the ion which tends to attract protons its acid strength is reduced from that of the uncharged species lt H2504 156 SelfIonization of Water a De ne selfionization Self Ionization is a reaction in which two like molecules react to give ions EX H2O H2O gt H30 b De ne the ionproduct constant for water The ionproduct constant for water is Kw Z H306 Z 66 at 25 C 0H 3 szz 157 Solutions of a Strong Acid or Base a Calculate the concentration of H3O in solutions of a strong acid 0 Calculate the concentration of hydronium ion at 25 C in 015M HN03 b Calculate the concentration of OH39 in solutions of a strong base 0 Calculate the concentration of hydroxide ion at 25 C in 010M CaOH2 158 The pH of a Solution a De ne pH The m is the negative of the base 10 logarithm of the molar hydronium ion concentration In an acidic solution H3O gt 10 x 10397 M In a neutral solution H3O 10 x 10397 M In a basic solution H3O lt 10 x 10397 M pH logH3O pOH logOH39 pH pOH 1400 b Calculate the pH from the hydroniumion concentration 0 Orange juice has a hydroniumion concentration of 29 x 10394 M o What is the pH C Calculate the hydroniumion concentration from the pH H3O 10quot o The pH of human blood is 740 What is the H30 Chapter 16 AcidBase Equilibria 161 AcidIonization Equilibria Write the chemical equation for a weak acid undergoing acid ionization in aqueous solution An acid reacts with water to produce H3O and the conjugate baseion HC2H302aq gt H30aq C2H30239aq De ne acidionization constant and degree of ionization The acidionization constant is the equilibrium constant for the ionization of a weak acid HAaq H20 gt H3Oaq A39aq H 3 230 Z 9 lt A6 3 Z Z K022 The degree of ionization of a weak electrolyte is the fraction of molecules that react with water to give ions May also be expressed as a percentage males that ionized x De ree of ionization 9 moles started wzth Determine Ka from the solution pH 0 A solution that is 0012 M HC6H4N02 has a pH of 339 at 25 C 0 What is the Ka and degree of ionization of HC6H4N02 d Calculate concentrations of species in a weak acid solution using Ka 1 Approximation method 0 What are the concentrations of HC6H4N02 hydronium ion and nicotinate ion in a solution of 10 M HC6H4N02 Ka 14 x 10395 o What is the pH and degree of ionization 2 Quadratic Formula 0 What is the pH at 25 C of 0036 M HC9H7O4 Ka 33 x 10394 State the assumption that allows for using approximations when solving problems If the concentration of the acid Ca divided by Ka equals 100 or more because it gives an error of less that 5 162 Polyprotic Acids State the general trend in the ionization constants of a polyprotic acid In general the second ionization constant Kaz of a polyprotic acid is much smaller than the rst ionization constant Kal Calculate concentrations of species in a solution of a diprotic acid H2C6H506 is a diprotic acid What is the pH of a 010 M solution 0 What is the concentration of C6H606239 o Ka1 79 x 10395 Ka2 16 x 103912 163 BaseIonization Equilibria a Write the chemical equation for a weak base undergoing ionization in aqueous solution Baq H20 gt HBaq OH39aq HB Z 9 6 OHquot b De ne baseionization constant The baseionization constant is the equilibrium constant for the ionization of a weak base c Calculate concentrations of species in a weak base solution using Kb o What is the pH of a 00075 M solution of C17H19N03 at 25 C 0 Kb 16 x 10396 164 Acid Base Properties of Salt Solutions a Write the hydrolysis reaction of an ion to form an acidic solution The hydrolysis of an ion is the reaction of an ion with water to produce the conjugate acid and hydroxide ion or the conjugate base and hydronium ion Ex NH4aq H20 gt NH3 H3Oaq b Write the hydrolysis reaction of an ion to form a basic solution Ex CN39aq H20 gt HCNaq OH39aq c Predict whether a salt solution is acidic basic or neutral The anions of weak acids are basic F39 NOz39 CN39 CHgOO39 HPO4239 The anions of strong acids are neutral CI39 Br39 I39 NO339 CIO439 The anions of polyprotic acids are acidic HSO439 H2PO439 The cations of weak bases are acidic NH4 The cations of strong bases are neutral Li Na K Ca 1 A salt of a strong base and a strong acid The salt has no hydrolysable ions and so gives a neutral solution EXNaCI Na H20 gt no reaction Cl39 H20 gt no reaction 2 A salt of a strong base and a weak acid The anion of the salt is the conjugate base of the weak acid It hydrolyzes to give a basic solution EXNaCN Na H20 gt no reaction CN39 H20 gt HCN OH39 3 A salt of a weak base and a strong acid The cation of the salt is the conjugate acid of the weak base It hydrolyzes to give an acidic solution Ex NH4C NH4 H20 gt NH3 30 Cl39 H20 gt no reaction 4 A salt of a weak base and a weak acid Both ions hydrolyze If Ka of cation is larger the solution is acidic If Kb of anion is larger the solution is basic Obtain Ka from Kb or Kb from Ka KaszKw KW 10 x 103914 Calculate concentrations of species in a salt solution 0 What is the pH of 010 M sodium nicotinate at 25 C 0 The Ka 14 x 10395 165 Common Ion Effect Explain the commonion effect The commonion effect is the shift in an ionic equilibrium caused by the addition of a solute that provides an ion that takes part in the equilibrium b Calculate the commonion effect on acid ionization effect of a strong acid 0 The degree of ionization of acetic acid HC2H302 in a 010 M solution at 25 C is 0013 K 17 x 10395 0 Calculate the degree of ionization of HC2H302 in a 010 M solution to which suf cient HCI is added to make it 0010 M HCI c Calculate the commonion effect on acid ionization effect of a con base 0 A solution is 010 M HC2H302 and 020 M NaC2H302 Ka 17 x 10395 o What is the pH of this solution at 25 C 166 Buffers a De ne buffer and buffer capacity and buffer range A buffer is a solution characterized by the ability to resist changes in pH when limited amounts of acid or base are added to it Buffer cabacitv is the amount of acid or base the buffer can react with before giving a signi cant pH change Depends on the amount of acid and conjugate base in solution Uness the ratio of amount of acid to amount of conjugate base is close to 1 the buffer capacity will be too low to be useful Describe the pH change of a buffer solution with the addition of acid or base When a strong acid is added to the buffer it supplies hydronium ions that react with the base A39 H30 A39 gt HA H20 When a strong base is added to the buffer it supplies hydroxide ions that react with the acid HA OH39 HAgt H20 A39 Calculate the pH of a buffer from give volumes of solution 0 You mix 60mL of 0100 M NH3 with 40mL of 0100 M NH4CI o What is the pH of this buffer d Calculate the pH of a buffer when a strong acid or base is added 0 Calculate the pH of 75mL of a buffer solution of 010 M HC20302 and M NaC20302 TO Of M HCI is added e HendersonHasselbalch Equation base acid pHpK0log 167 Acid Base Titration Curves a De ne equivalence point The equivalence point is the point in a titration when a stoichiometric amount of reactant has been added b Describe the curve for the titration of a strong acid by a strong base An acidbase titration curve is a plot of the pH of a solution of acid or base against the volume of added base or acid For the titration of a strong acid by a strong base The pH changes slowly until the molar amount of base nearly equals that of the acid equivalence point At the equivalence point the pH is 70 C Calculate the pH of a solution of a strong acid and a strong base 0 Calculate the pH of a solution in which 10mL of 0100 M NaOH is added to 25mL of 0100 M HCI Describe the curve for the titration of a weak acid by a strong base The titration starts at a higher pH because it is a weak acid The pH changes slowly at rst then rapidly near the equivalence point The equivalence point is on the basic side Calculate the pH at the equivalence point in the titration of a weak acid by a strong base 0 Calculate the pH of the solution at the equivalence point when 25mL of 010 M nicotinic acid is titrated by 010 M NaOH Ka 14 x 10395 f Describe the curve for the titration of a weak base by a strong acid The pH declines slowly at rst then falls abruptly between pH 7 3 e Calculate the pH of a solution at several points of a titration of a weak base by a strong acid 0 You titrate a 25mL sample of 0100 M NH3 by 0100 M HCI Calculate the pH of the NH3 solution a Prior to the addition of any HCL b After the addition of 12mL of HCI c At the equivalence point
Are you sure you want to buy this material for
You're already Subscribed!
Looks like you've already subscribed to StudySoup, you won't need to purchase another subscription to get this material. To access this material simply click 'View Full Document'