Chem 162-2011 Lecture 7

Chem 162-2011 Lecture 7 - CHEMISTRY 162-2011 LECTURE 7...

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CHEMISTRY 162-2011 LECTURE 7 ANNOUNCEMENTS E-MAIL ATTENDANCE Sign in EXAM    Wednesday, Feb. 16 th , 9:40-11:00 PM      Chapters 12.1 - ? QUIZ Chem 162-2011 Lecture 7 1
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PLAN FOR TODAY : CHAPTER 14.1 – 14.3 CHEMICAL EQUILIBRIUM The dynamic nature of equilibrium The equilibrium constant expression Modifying equilibrium constant expressions Chem 162-2011 Lecture 7 2
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CHAPTER 14 - CHEMICAL EQUILIBRIUM A + B C + D (gases or solutes, only) Law of mass action (or molar interaction ): K c = ([C][D])/([A][B]) 2A + 3B 4C + 1D A + A + B + B + B C + C + C + C + D K c = ([C] • [C] • [C] • [C] • [D])/( [A] • [A] • [B] • [B] • [B]) K c = ([C] 4 [D])/([A] 2 [B] 3 ) eA + fB gC + hD K c = ([C] g [D] h )/([A] e [B] f ) e.g., 2NO + O 2 2NO 2 K c = ([NO 2 ] 2 )/([NO] 2 [O 2 ]) K A B [B]/[A] = K 1 C D [D]/[C] = K 2 A + C B + D ([B][D])/([A][C]) = K Addition of ([B]/[A]) + ([D]/[C]) = (([B][C] + [A][D]))/([A][C]) Equations K(s) Add Multiply Reverse Invert Double Square Halve Square root K p inatm = K c inM (RT) ∆ngas Chem 162-2011 Lecture 7 3
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Previously in this class: We showed all chemical reactions going to completion. Now:  We’ll show reactions which don’t go to completion, i.e., which  come to equilibrium.  In fact, all reactions we will study are in  closed systems, and therefore come to equilibrium. Chem 162-2011 Lecture 7 4
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UNDERSTANDING EQUILIBRIA DYNAMIC* EQUILIBRIUM (*not static equilibrium) ET: At equilibrium, the forward and reverse reactionS proceed at equal rates and the concentrations of reactants and products remain constant. Mountain INITIALLY Slum sad k 1 = 0.01/s k -1 = 0.10/s town with Palacial happy 0 sad town with people/mi 2 1100 happy people/mi 2 Forward rate pre-equilibrium = k 1 x reactant conc. = 0.01s -1 x 1100 = 11 people/mi 2 s -1 Reverse rate pre-equilibrium = k -1 x reactant conc. = 0.10s -1 x 0 = 0 people/mi 2 s -1 Mountain AT EQUILIBRIUM Slum sad k 1 = 0.01/s k -1 = 0.10/s town with Palacial happy 100 sad town with people/mi 2 1000 happy people/mi 2 Equilibrium reached Macroscopically : You continuously see 1000 happy people on the left and 100 sad people on the right. Microscopically : You also see a constant equal exchange of sad people and happy people going across the bridge, a “dynamic equilibrium”. That is, the rate forward equals the rate reverse. Rate forward = k 1 x [reactant] = 0.01s -1 x 1000 = 10 people/mi 2 s -1 Rate reverse = k -1 x [product] = 0.10s -1 x 100 = 10 people/mi 2 s -1 Also note: K = [Products]/[Reactants] = 100/1000 = 0.1 K = k 1 /k -1 = 0.01/0.10 = 0.1 Chem 162-2011 Lecture 7 5
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UNDERSTANDING EQUILIBRIA Blue circles = Pentane Red circles = Hexane Chem 162-2011 Lecture 7 6 Dynamic equilibrium
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Chem 162-2011 Lecture 7 7 UNDERSTANDING EQUILIBRIA FREEZING POINT DEPRESSION LIQUID AND SOLID WATER AT EQUILIBRIUM AT 0 o C (FREEZING POINT) SALT ADDED TO H 2 O (NOTE FEWER MOLECULES OF H 2 O GOING INTO SOLID PHASE) Dynamic equilibrium Not at equilibrium
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UNDERSTANDING EQUILIBRIA DYNAMIC EQUILIBRIUM Fe 3+ + CNS - FeCNS 2+ Chem 162-2011 Lecture 7 8
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Chem 162-2011 Lecture 7 - CHEMISTRY 162-2011 LECTURE 7...

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