Final Exam: know your section, bring your ID!

Transcription

1 Chapter 15: Equilibrium Part 1 Read: BLB HW: BLB 15:13,14, 21 Supplemental 15:1 4 Know: Chemial Equilibrium Catalysts Equilibrium Constant Equilibrium onstant expression Homogeneous/Heterogeneous Equilibria Relationship between K p and K! n K K (RT) p Chemial Equilibrium Equilibrium is ahieved when opposing proesses proeed at equal. Whih equilibria have we previously disussed?? FINAL DEADLINE for redit on skill hek tests: Final Exam: know your setion, bring your ID! If a system is at equilbrium, what happens to the onentrations of reatants and produts over time? Is Equilibrium always ahieved quikly? Dr. Lori S. Van Der Sluys Page 1 Chapter 15 Dr. Lori S. Van Der Sluys Page 2 Chapter 15

2 N 2 (g) + 3H 2 (g) Haber proess 2NH 3 (g) Catalysts do not effet equilibrium onentrations. A B o n e n t r a t i o n Initial State: reatants only Equilibrium ahieved Time!" Time!" Initial state: produts only Final State: ratio of produts to reatants is the same for both! Note: The relationship between the onentrations of produts and onentrations of reatants at equilibrium will be the same regardless of starting onditions. Dr. Lori S. Van Der Sluys Page 3 Chapter 15! A atalyst lowers the ativation barrier between the reatants and produts! Lowering the ativation energy inreases the rate of a reation, both forward and bakward! The atalyst inreases the rate at whih equilibrium is ahieved, but it does not hange the omposition of the equilibrium mixture. Dr. Lori S. Van Der Sluys Page 4 Chapter 15

3 The Equilibrium Constant Sine the onentrations of reatants and produts don't hange over time at equilibrium, what is true about the ratio of onentrations? In general: Example: ja + kb R A [ ] p [ S] q [ ] j [ B] k pr + qs 2A B (2NO N 2 O 4 ) [ B] [ A] onstant " K [ N O 2 4 ] 2 eq [ NO] 2 is the equilibrium onstant for the reation. It is a NUMBER. What is the equilibrium onstant expression for the Haber proess? N 2 (g) + 3H 2 (g) 2NH 3 (g) ? [ ][ H 2 ] [ ] 2 N 2 NH 3 [ ][ H 2 ] 3 [ ] 2 N 2 NH 3 [ NH 3 ] 2 [ N 2 ][ H 2 ] 3 [ NH 3 ] 2 [ N 2 ] 2 [ H 2 ] [ NH 3 ] [ N 2 ][ H 2 ] is a funtion of temperature only. Dr. Lori S. Van Der Sluys Page 5 Chapter 15 Dr. Lori S. Van Der Sluys Page 6 Chapter 15

4 USING AN EQUILIBRIUM CONSTANT Information that an be obtained from K 1. Whih are favored? Amounts an be expressed in terms of onentrations or pressures: K K R A [ ] p [ S] q [ ] j [ B] k What units are denoted by square brakets? 2. Predit diretion of a reation 3. Obtain equilibrium onentrations of reatants and produts. K p K p p p R p j A p p What units are denoted by P x? How are K p and K related? K p K (RT) q S B k! n where #n n prod $ n reat When given how do I know if it is K or K p? If onentrations are given in M, then K If onentrations are given in P, then K p Dr. Lori S. Van Der Sluys Page 7 Chapter 15 Dr. Lori S. Van Der Sluys Page 8 Chapter 15

5 N 2 (g) + 3H 2 (g) 2NH 3 (g) In the Haber proess above, the following equilibrium onentrations of NH 3, N 2, and H 2 were determined at 472 C. [H 2 ] M [N 2 ] M [NH 3 ] M Find K and K p. When omparing reations, find out how the equilibrium onstants ( ) are related: Example; At a ertain temperature, K for the following reation is 16. I H 2 (g) + I 2 (g) 2HI(g) At the same temperature, what is K for this reation? II HI(g) 1/2 H 2 (g) + 1/2 I 2 (g) 1. 1/ / there is not enough information to answer this question. Dr. Lori S. Van Der Sluys Page 9 Chapter 15 Dr. Lori S. Van Der Sluys Page 10 Chapter 15

6 Heterogeneous Equilibria involves reatants and produts in more than one phase 3Fe(s) + 4H 2 O(g) Fe 3 O 4 (s)+4h 2 (g) What are the equilibrium onstant expressions (K p and K ) for these reations? [ ][ H 2 ] 4 [ ] 3 [ H 2 O] 4 Fe O 3 4 Fe AgCl(s) Ag + (aq) + Cl $ (aq) What is [Fe]? [Fe 3 O 4 ]? C 6 H 6 (g) + 3H 2 (g) C 6 H 12 (g). K [ Fe] 3 [ Fe 3 O 4 ] K [ H 2] 4 eq [ H 2 O] 4 % onstant Leave solids and pure liquids out of the equilibrium onstant expression. CaCO 3 (s) NaOH(aq) + HCl(aq) CaO(s) + CO 2 (g) NaCl(aq) + H 2 O(l) Dr. Lori S. Van Der Sluys Page 11 Chapter 15 Dr. Lori S. Van Der Sluys Page 12 Chapter 15

7 General Approah to Equilibrium Constant Problems 1) Write the balaned reation. 2) Write the general form for. 3) Set up a data table (ie table): (may need algebrai unknowns) $initial onditions $hanges in onentrations $equilibrium onentrations 1.00 mole of SO 2 (g) and 1.00 mole of O 2 (g) are added to a 1.00 L ontainer and reat until equilibrium is ahieved. At equilibrium, the ontainer has moles of SO 3 (g). Find K at 1000K. 4) Substitute equilibrium onentrations into the expression for and solve. Dr. Lori S. Van Der Sluys Page 13 Chapter 15 Dr. Lori S. Van Der Sluys Page 14 Chapter 15

8 What is K p at the same temperature? 2SO 2 (g) + O 2 (g) 2SO 3 (g) A one L ontainer holds 224g of Fe and 5.00 mole of H 2 O(l). It is heated to 1000K and reahes equilibrium. 56g of Fe are left unreated. What is K at 1000K? 3Fe(s) + 4H 2 O(g) Fe 3 O 4 (s) + 4H 2 (g) i e [ ] 4 [ ] 4 K H 2 H 2 O Dr. Lori S. Van Der Sluys Page 15 Chapter 15 Dr. Lori S. Van Der Sluys Page 16 Chapter 15