CHM1046 EXAM 3 STUDY GUIDE Key Equations Chapter 16 Definition of Pka o p K a log K a Henderson Hasselbalch Equation o pH p K a log Conjugate Base Acid Chapter 17 S k ln W o Relating entropy to number of microstates Suniv Ssys Ssurr 0 o Second law of thermodynamics spontaneous process Suniv Ssys Ssurr 0 o Second law of thermodynamics equilibrium process Srxn nS products mS reactants o Standard entropy change of a reaction G H T S o Free energy change at constant temperature Grxn n Gf products m G f reactants o Standard free energy change of a reaction G G RT lnQ o Relationship between free energy change and standard free energy change and o Relationship between standard free energy change and the equilibrium constant reaction quotient G RT ln K Chapter 18 E Cell Ecathode Eanode G nFEcell G nFE cell E cell 0 0257 V n ln K E cell 0 0592V n log K E E 0 0257 V n ln Q o Calculating the standard emf of a galvanic cell o Relating free energy change to the emf of the cell o Relating the standard free energy change to the standard emf of the cell o Relating the standard emf of the cell to the equilibrium constant o Relating the standard emf of the cell to the equilibrium constant o Nernst Equation Relating the emf of the cell to the concentrations under nonstandard state conditions E E 0 0592 n log Q o Nernst Equation Relating the emf of the cell to the concentrations under nonstandard state conditions Chapter 16 Concepts Common Ion The same or common ion that appears in a solution with two dissolved solutes Common Ion Effect The shift in equilibrium caused by the addition of a compound having an ion in common with the dissolved substance o Plays an important role in all problems that determine the pH of a solution and molar solubility o The presence of a common ion decreases the solubility of a slightly soluble salt o Le Ch telier s Principle Other name for the common ion effect Buffer Solutions A combination of either a weak acid and its weak conjugate base or a weak base and its weak conjugate acid o A buffer solution reacts with small amounts of added acid or base in such a way that the pH of the solution doesn t change pH at Equivalence Points o Strong acid Strong base titrations pH at equivalence point 7 o Weak acid Strong base titrations pH at equivalence point 7 o Strong Acid Weak base titrations pH at equivalence point 7 Acid Base Indicators Weak organic acids or bases that change color near their equivalence point in an acid base neutralization reaction o End Point The point in a titration when the indicator changes color Solubility Product KSP Expresses equilibrium between a solid precipitate and its ions in solution o Solubility can be calculated from KSP o KSP can be calculated from Solubility Molar Solubility Moles of solute divided by the amount of Liters solution Solubility Grams of solute divided by the amount of liters solution The solubility of salts with anions derived from strong acids are unaffected by pH o AgCl Ag aq Cl aq not affected by an acid solution o Because Cl is the conjugate base of a strong acid HCI the solubility of AgCl is Formation Constant Kf The equilibrium constant for the complex ion o Kf is used to measure the tendency of a metal ion to form a particular complex formation ion o Also called stability constant o Larger Kf More stable the complex ion Complex Ions An ion containing a central metal cation bonded to one or more molecules or ions o Complex Ions are formed in solution by the combination of a metal Cation with a Lewis base The formation constant Kf measures the tendency toward the formation of a specific complex ion o Complex ion formation can increase the solubility of an insoluble substance Qualitative Analysis The identification of cations and anions in solution Chapter 17 Concepts Entropy A measure of the different ways a system can disperse its energy Any spontaneous process must lead to a net increase in entropy in the universe second law of thermodynamics Standard Entropy of Reaction Srxn Calculated by the difference in standard entropies between products and rectants o Srxn n S products m S reactants Standard Free Energy of Reaction Grxn The free energy change for a reaction when it occurs under standard state conditions when reactants in their standard states are converted to products in their standard states Standard Free Energy of Formation The free energy change that occurs when 1 mole of the compound is synthesized from its elements in their standard states Third Law of Thermodynamics The entropy of a perfect crystalline substance is zero at 0 K This law enables us to measure the absolute entropies of substances Under conditions of constant temperature and pressure the free energy change G is less than zero for a spontaneous process and greater than zero for a nonspontaneous process o G 0 Spontaneous Process o G 0 Nonspontaneous Process o G 0 Equilibrium Process o G H T S Chemical or Physical Process at Constant Temp and Pressure This last equation can be used to predict the spontaneity of a process H S and G are state functions o If H is negative and S is positive then G will always be negative regardless of temperature o If H is negative and S is negative then G will be negative only when T S is smaller in magnitude than H This condition is met when T is small Standard Free Energy Change for a Reaction G Can be calculated from the standard free energies of formation of reactants and products o Free Energy The energy available to do work o Gibbs Free Energy Other name for Free Energy The equilibrium constant k of a reaction and the standard free energy change of the reaction G are related by the equation G RT ln K Many biological reactions are nonspontaneous and are driven by the hydrolysis of ATP for which G is negative Chapter 18 Redox Reactions Reactions that involve the transfer of electrons Any equation representing redox processes can be balanced using the ion electron method o All electrochemical reactions involve the transfer of electrons and are therefore redox reactions Anode The electrode at which oxidation occurs in a galvanic cell Cathode The electrode at which reduction occurs in a galvanic cell Half Cell Reactions Oxidation and Reduction reactions at the electrodes Cell Voltage The voltage across the electrodes of a galvanic cell o Also known as Cell Potential o Also known as Electromotive Force emf Galvanic Cell A cell in which electricity is produced by a spontaneous chemical reaction Oxidation and
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