CHEM 1415 1st EditionLecture 17Unit: Equilibrium ConcentrationOutline of Current Lecture I. Equilibrium Concentrationsa. Example 1II. LeChatelier’s Principle a. Effects of a Change in Concentrationb. Effects of a Change in Pressurec. Effects of a Change in Temperatured. Effects of a CatalystCurrent Lecture Equilibrium Concentrationso Strategies to solve equilibrium concentration problems Write a balanced chemical equation for the relevant equilibrium or equilibria Write the corresponding equilibrium expression Create a table of concentrations for all of the reacting specieso Example 1 Phosphorus trichloride reacts with Chlorine gas to form phosphorus pentachloride at k = 33, T = 250℃, 0.050 M of PC l3 and 0.015 M of Cl2. What are the equilibrium concentrations ? -Cl2 (g)+PCl3 (g)←→PCl5 (g)-K=[ PCl5]2[Cl2][ PC l3]=33Cl2PCl3PCl5Initial Concentration0.015 M 0.050 M 0 MChange in Concentration-x -x +xFinal 0.015 - x 1.50 - x xThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Concentration-PCl[¿¿5][Cl2][PC l3]=33K =¿ = x(0.050−x)(0.015−x)=59.3-33 x2−3.145 x +0.025=0-x=0.087∨0.0088- Therefore [PCl5]=x=0.0088 M ,-[C l2]=0.015−x=0.015−0.0088=.006 M ,-[PC I3]=0.05−x=0.050−0.0088=0.042 M LeChatelier’s Principleo When a system at equilibrium is stressed, it responds by reestablishing equilibrium to reduce the applied stresso Effects of a Change in Concentration by considering the reaction quotient, Q withthe equilibrium constant, KType of Concentration ChangeResulting Change in Q Response of SystemProducts increased Q > K More reactants formedProducts decreased Q < K More products formedReactants increased Q < K More products formedReactants decreased Q > K More reactants formedo Effects of a change in Pressure on Equilibrium If number of moles of gases differs between reactants and products, a shift in pressure will result in a change in the equilibrium positiono Effects of change in temperature on equilibriumo Effect of o Effects of a catalyst on Equilibrium Has no effectType of Reaction Type of Temperature Change Response of SystemExothermic T increase More reactants formedExothermic T decrease More products formedEndothermic T increase More products formedEndothermic T decrease More reactants
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