lec12_whc - Announcements Regrades by the end of discussion...

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Announcements • Regrades – by the end of discussion – Random photocopying of exams • Chapter 15 – Chemical Equilibrium
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Last Time • Equilibrium; K • Equilibrium constant – Concentration – K c – Pressure – K p • Hess “like” law to manipulate K • Disequilibrium and Reaction Quotients –Q versus K
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Last time: Pure Liquids and Solids • Equilibrium constant expressions do not contain concentration terms for solid or liquid phases of a single component (that is, pure solids or liquids). C(s) + H 2 O(g) CO(g) + H 2 (g); K c = 1 × [H 2 O(g)] [CO] [H 2 ] e.g. NaCl(s) + H 2 O(l) Na + (aq) + Cl - (aq) + H 2 O(l) Water not pure anymore, but 55.55 mol/L hardly changed. The mole fraction remains 1.0! e.g. Pure solids and liquids have activities of 1 K c 1 × 1 [Na + (aq)] [Cl - (aq)] × 1
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• Reaction quotient (Q) -Mathematically the same as K’s except non–equilibrium parameters are used Disequilibrium • Q predicts the direction of the reaction: If, Q < K there are insufficient products and the reaction proceeds to the right as written If, Q > K there is too much product. The reaction proceeds to the left as written (i.e., in reverse)
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Equilibrium, K eq Disequilibrium, Q
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The equilibrium constant for the reaction of hydrogen gas with iodine gas to form HI(g) is K c = 48.9. Example 15E – Approaching Equilibrium The concentrations at a given time during the reaction are measured at [H 2 ] = 2.8x10 –2 mol/L, [I 2 ] = 8.9x10 –3 mol/L, and [HI] = 1.45x10 –3 mol/L. Is this reaction at equilibrium? If not, how will the chemistry change to achieve equilibrium?
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H 2 (g)+I 2 (g) 2HI(g); K c = 48.9 [H 2 ] = 2.8x10 –2 mol/L, [I 2 ] = 8.9x10 –3 mol/L, and [HI] = 1.45x10 –3 mol/L. Solution 15E – Approaching Equilibrium Q c = = = 8.4 x 10 -3 < K c =48.9 [H 2 ][I 2 ] [HI] 2 2.8x10 –2 x 8.9x10 –3 ( 1.45x10 –3 ) 2 Q must increase to reach K. The reaction proceeds to the right as written to make more product and increase Q.
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This note was uploaded on 06/13/2010 for the course CHEM 995940767 taught by Professor Topadakis during the Spring '10 term at UC Davis.

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lec12_whc - Announcements Regrades by the end of discussion...

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