Chapter 14 14 1 14 2 Know how to write the expressions of Kp and Kc for both homogeneous and heterogeneous equilibriums Homogenous equilibrium applies to reactions in which all reacting species are in the same phase These are the equilibrium partial pressures in atm of NO2 and N2O4 In general Kc isn t equal to Kp because the partial pressures of reactants and products aren t equal to their concentrations expressed in moles per liter Their relationship can be found as Heterogeneous equilibrium results from a reversible reaction involving reactants and products that are in different The new equilibrium constant is conveniently displayed as a single concentration The value of Kc isn t dependent on how much CaCO3 and CaO are present as long as some of each are present at equilibrium Kp PCO2 Equilibrium constant is equal to the pressure of CO2 gas in this example Know the different forms of K and how to use Hess s law to find the equilibrium constant of the overall equilibrium using multiple equilibria Ex N2O4 g 2NO 2 g Kc NO2 2 N2O4 P2 No2 P N204 KP Kp Kc 0 0821T n phases Ex CaCO3 s CaO s CO 2 g Kc CaO CO2 CaCO3 CaCO3 CaO K C Kc CO2 A B C D K C C D E F K C Overall Reaction A B E F k C Kc C D A B Kc E F C D Kc K c K C Example with Hess s Law At certain temperatures the following reactions have the equilibrium constant 1 S s O2 g 2S s 2O 2 2S s 3 2 g 2SO 3 g K2 9 8 10 128 2 g K1 4 2 10 52 1 K1 2 K2 K 1 4 2 1052 2 9 8 10 128 For any reaction at equilibrium there is an equilibrium constant k K Products x Reactants y X and Y are equal to their stoichiometric coefficient K 5 6 10 23 Lecture Notes aA bB cC dD C D D k C K Equilibrium will lie to the right and favors products K 1 Equilibrium will lie to left and favor reactants Equilibrium constants are unitless Writing Equilibrium Constant Expressions 1 The concentrations of the reacting species in the condensed phase are expressed in M In the gaseous phase the concentrations can be expressed in M or in atm 2 The concentrations of pure solids pure liquids and solvents do not appear in the equilibrium constant expressions 3 The equilibrium constant is a dimensionless quantity 4 In quoting a value for the equilibrium constant you must specify the balanced equation and the temperature 5 If a reaction can be expressed as a sum of two or more reactions the equilibrium constant for the overall reaction is given by the product of the equilibrium constants of the individual reactions 14 4 Know how to predict the direction of the reaction Qc vs Kc the equilibrium constant Kc expression IF Qc Kc system proceeds from left to right to reach equilibrium Qc Kc the system is at equilibrium Qc Kc system proceeds from right to left to reach equilibrium The reaction quotient Qc is calculated by substituting the initial concentrations of the reactants and products into Know how to use I C E table to find different unknowns equilibrium concentrations of the products initial concentration of the reactants or equilibrium constant Lecture Notes Calculating Equilibrium Concentrations 1 Express the equilibrium concentrations of all species in terms of the initial concentrations and a single unknown x which represents the change in concentration 2 Write the equilibrium constant expression in terms of the equilibrium concentrations Knowing the value of the equilibrium constant solve for x 3 Having solved for x calculate the equilibrium concentrations of all species 14 5 Understand Le Ch telier s principle Stress Types 1 Concentration 2 Pressure 3 Volume 4 Temperature Concentration Changed Principle States that if an external stress is applied to a system at equilibrium the system adjusts in such a way that the stress is partially offset as the system reaches a new equilibrium position Be able to know how the equilibrium would shift in case of any stress added to the system Change Shifts the Equilibrium Increase concentration of product s left Decrease concentration of product s right Decrease concentration of reactant s right Increase concentration of reactant s left Volume and Pressure Change Shifts the Equilibrium Increase pressure Side with fewest moles of gas Decrease pressure Side with most moles of gas Decrease volume Side with most moles of gas Increase volume Side with fewest moles of gas Temperature Change Exothermic Rxn Endothermic Rxn Increase temperature left Right Decrease temperature Right Left Be able to know which stress will affect the equilibrium constant temperature only and how it will affect it Temperature increase favors endothermic reaction temperature decrease favors exothermic direction Chapter 15 15 1 15 2 Know how to identify the conjugate Br nsted acid base pair in equilibrium Bronsted acid is a substance capable of donating a proton and a Bronsted Base is a substance that can accept a proton An extension of the Br nsted definition of acids and bases is the concept of the conjugate acid base pair which can be defined as an acid and its conjugate base or a base and its conjugate acid The conjugate base of a Br nsted acid is the species that remains when one proton has been removed from the acid Conversely a conjugate acid results from the addition of a proton to a Br nsted base Every Br nsted acid has a conjugate base and every Br nsted base has a conjugate acid For example the chloride ion Cl is the conjugate base formed from the acid HCl and H3O hydronium ion is the conjugate acid of the base H2O HCl H2O cid 224 H 3O Cl Know how to use the ion product Kw to find H or OH concentrations Equilibrium constant for autoionization of water is Kc H3O OH which is the same as Kc H OH To indicate that the equilibrium constant refers to the autoionization of water replace Kc with Kw Kw H3O OH H OH Kw is called the ion product constant which is the product of the molar concentrations of H and OH ions at a particular temperature Here 25 C Whenever H OH the aqueous solution is said to be neutral In an acidic solution there is an excess of H ions and H OH In a basic solution there is an excess of hydroxide ions so H OH 15 3 15 7 Memorize the six strong acids H2SO4 HClO4 HI HBr HCl HNO3 Memorize the following three strong bases KOH NaOH Ba OH 2 Understand what the difference between strong and weak acid is strong acid dissociates completely in water while weak acid reaches equilibrium Strong acids are strong electrolytes that for practical purposes are assumed to ionize completely in water Most of the strong acids are inorganic acids hydrochloric acid
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