Chapter 13 Notes
Popular in General Chemistry II
Popular in Chemistry
This page Class Notes was uploaded by Alex Grauherr on Tuesday February 23, 2016. The Class Notes belongs to 132 at Central Michigan University taught by MCGUIRK in Winter 2016. Since its upload, it has received 20 views. For similar materials see General Chemistry II in Chemistry at Central Michigan University.
Reviews for Chapter 13 Notes
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: 02/23/16
Chapter 13 Notes 0 Chemical equilibrium is the state when concentrations of reactants and products no longer change 0 Reactions occur on both forward and reverse directions 0 When the forward and reverse reactions react at the same rate concentrations stay the same and the reactions are at their equilibrium 0 The equilibrium mixture is the mixture of products and reactants in their equilibrium state 131 The Equilibrium State 0 Many reactions do not react to completion 5 Ireaetainta E reactants E eli i 4 1 5 s s a g i ezqtnllbrlum equlllllmbrmm E g D g Q quot Z 1 b 3 t l E i i ri m products I r pr du s 111 11 IS T lquot Tr IF39T39IE quotTHE reached when concentrations become constant values film 3111 reaction Reac nn rate EQU itIIium ackward reac nn Time Equilibrium state can also be reached when reactants and products concentrations quit changing rates and become equal Use a double arrow to show a reaction can go in reverse ABlt gtAB 0 Reactants will be used for substances on the left AB 0 Products will be used for substances on the right All chemical reactions are reversible but irreversible reactions are those that almost reach completion The equilibrium mixture contains mostly products and a few reactants The reverse reaction is often too slow to notice When equilibrium values are reached the reaction doesn t stop concentrations just become constant values and the rates of forward and reverse reactions become equal Reaction rates depend on concentrations so the rate of the forward reaction decreases as the reactants decrease and the reverse reaction increases as the concentrations of products increase The rate of the decreasing forward reaction eventually becomes equal to the rate of the increasing reverse reaction and there will be no more change in concentrations and also no net conversion of reactants to products 132 The Equilibrium Constant Kg Norwegian chemists Cato Maximilian Guldberg and Peter Wage proposed the equilibrium equation shows that the concentraions are equal in an equilibrium mixture The equilibrium constant expression is the right side of the equilibrium equation and the equilibrium constant KC is on the left C lchld Equilibrium Equation for aAbBcCdDz KC W Square brackets are used to indicate molarity KC Subscript C means concentration The substances in the equilibrium equation can be gases or molecules and ions in a solution however pure solids and liquids are not included Concentration was previosly called active mass so the equilibrium equation may also be referred to as the Law Of Active Mass Equilibrium constant KC the number obtained by evaluating the equilibrium equation The equilibrium constant for a reaction at a particular temperature always has the same value KC has no dimensions when recorded because they cancel out in the equation Equilibrium constants are temperature dependant so the temperature must be recorded with the KC value 133 The Equilibrium Constant KB 0 KP is used for partial pressures instead or molar concentrations 0 The equilibrium constant KP is used for reactions of gases defined using partial pressures 0 Also dimensionless PAVnART so PAnAVRT 0 This is the reaction for A reactions for BC and D are similar Overall Equation d D B KP x RT gtcd ab a A V KC and KP are related b KPKCRTAn cd ab An 0 KP only equals KC if the number of moles of gases appear on both sides of the balanced chemical equation making An0 134 Heterogeneous Equilibria 0 An equilibria in which all reactants and products are in a single phase is 0 They are usually found in either gaseous phase or in solution 0 In reactants and products are present in more than on phase 0 The concentrations of pure solids and pure liquids are not included in equilibria equations 0 Only concentrations of gases and solutes in solutions Will be included because their concentrations can vary While pure solids and liquids concentrations do not 0 If temperature is changed the concentration and pressure Will change as well values of KC and KP depend on temperature 135 Using the Equilibrium Constant Judging the extent of a reaction The equilibrium constant measure how far a reaction proceeds before equilibrium 0 A large number means the reaction nearly reaches completion 0 A small number means equilibrium ratio of products to reactants is very small and equilibrium is reached quickly KC gt 103 0 Products greater than reactants 0 Reaction nears completion KClt 103 O Reactants greater that products 0 Reaction barely proceeds before reaching equilibrium Kcis between 10393 and 103 0 Both reactants and products are present at equilibrium Predicting the Direction of 3 Reaction The reaction quotient is similar to the equilibrium constant KC but concentration values may not be at equilibrium During a reaction Q Will eventually equal KC QClt KC Q will help to predict the direction of a reaction 0 Forward reaction 0 Towards equilibrium increasing 1 QcgtKCI 0 Reverse reaction 0 Towards equilibrium decreasing 39 QCKC3 0 At equilibrium 0 No net reaction Calculating Equilibrium Concentrations If all but one concentration is known you can find the unknown directly from the equilibrium equation If initial concentrations are known but equilibrium concentrations are not you can use an ICE table 0 ICE mean Initial Change Equilibrium 0 To use the ICE table Begin with the balanced equation Make a list with each substance involved with 0 Initial concentration 0 Change in concentration to equilibrium 0 Equilibrium concentration Use X for change in concentration Plug concentrations into equilibrium equation and solve for X Calculate equilibrium concentrations from X Check by plugging into equilibrium equation 136 Le Chatelier s Principle 0 Le Chatelier s principle If stress is applied to a miXture at equilibrium net reaction occurs in the direction that relieves the stress 0 To alter the composition of an equilibrium mixture the concentration pressure volume or temperature can be changed 0 Changing any of these factors causes Le Chatelier s Principle 0 The composition of the mixture will change until the state of equilibrium is reached again 0 The reaction goes away from the side the stress was placed to reach equilibrium 137 Changes in Concentration 0 Le Chatelier s principle states that 0 If any stress is added in the form of concentration to reactants of product the stress is relieved by using the added substance going to the opposite side that the concentration was added 0 If any stress of concentrations is removed the reaction will go in the direction of the removal of concentration and the substance is replenished back to equilibrium 0 Color can be an indicator of concentration change when the mixture has colored reactants and products 138 Changes in Pressure and Volume 0 An increase in pressure by a decrease in volume will cause a decrease in the number of moles 0 A decrease in pressure by an increase in volume will cause an increase in the number of moles REMEMBER THAT PURE SOLIDS AND PURE LIQUIDS ARE IGNORED WHEN USING EQUILIBRIUM EQUATIONS FOR BOTH QC AND KC 139 Changes in Temperature 0 A change in temperature almost always changes the value of the equilibrium constant 0 The temperature depends on AH 0 If it s positive then the reaction is endothermic I Heat is added and the reaction shift right I Heat is lowered the reaction shifts right 0 If it s negative the reaction is exothermic I Heat is added and the reaction shifts left I Heat is lowered and the reaction shifts right 1310 The Effect of a Catalyst on Equilibrium 0 Catalysts increase the reaction rate my making more energy readily available 0 Catalysts lower the activation energy for forward and reverse reactions equally 0 The reaction will still reach equilibrium with a catalyst but at a faster rate
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'