1. Chemical EquilibriumQ, K, and Calculations Chapter 16

2. Equilibrium • the forward and reverse reactions proceed at equal rates • the concentrations of reactants and products are constant = • Can be reached from either direction (starting with either “reactants” or “products” has the same result) Example Reaction CH4 + H2O CO + 3H2

3. CO + 3 H2 CH4 + H2O

4. Q and K • Reaction Quotient: Q • Describes a rxn at _____________ • Equilibrium Constant: K • Describes a rxn at _____________ • Both values are calculated from the same expression

5. Equilibrium Constant Expression For a general reaction occurring __________: a A(aq) + b B(aq) c C (aq) + d D(aq) [ ] = molarity c

6. Equilibrium Constant Expressions • The exponents are based on the __________!! • ________ OVER _______ • There are no _____ for Q or K When writing the expressions • Include only these phases: ___ + ____ • Omit these phases: ____+ ____

7. For reactions of __________: a A(g) + b B(g) c C (g) + d D(g) c d a b Kp = PC PD PA PB P = partail pressure of the gas

8. Q and K • If concentrations or partial pressures represent the reaction atequilibrium, you can calculate ______. • If concentrations or partial pressures represent the reaction at any time, you can calculate ______.

9. Write the equilibrium expression 1) N2(g) + 3H2 (g) <----> 2NH3 (l) (Kp) 2) CO(g) + 3H2(g) <----> CH4(g) + H2O(g) (Kc & Kp)

10. 2 Red(g) <----> Blue (g) • Write the expression for Kc and Kp • Applet

11. Calculating K PCl3(g) + Cl2(g) <--> PCl5(g) Kc = [PCl5] [PCl3][Cl2] Different amounts of R & P are mixed at 546 K to determine K Comment on the equilibrium position.

12. Calculating K H2(g) + I2(g) <---> 2HI • At equilibrium, the concentration for both H2 and I2 = 0.0037 M and HI = 0.0276. Write the expression for K and calculate its value? What this value mean? • K > 1 the reaction is ________ favored • K< 1 the reaction is ________ favored

13. Calculating Q • H2(g) + I2(g) <---> 2HI • 2 moles each of H2 and I2 and 3 moles of HI are placed in a 0.5 L flask. Determine if the rxn is at equilbrium? If not will it move forward or reverse? • Q = K the reaction _______________ • Q < K the reaction ________________ • Q > K the reaction ________________

14. Kc and Kp are related • Kp = Kc(RT)∆n • R= 0.08206 Liter atm mol K • ∆n = # product gases - # reactant gases

15. Kp = Kc(RT)∆n • H2(g) + I2(g) <---> 2HI • If Kc = 56, calculate Kp at 25 °C.

16. A real one!Kp = Kc(RT)∆n • N2(g) + 3 H2(g) <---> 2NH3(g) • The Kp = 5.8 x105, calculate Kc at 25 °C.

17. MORE ABOUT K!!!! • K values for various forms of a balanced equation relate to the coefficients The K value for the reverse rxn is the ______________ Multiplying a reaction by a # _______________

18. MORE ABOUT K!!!! at 298 K C(s) + 1/2 O2(g) <---> CO(g) K1 = 4.6 X 1023 2 C (s) + O2 (g) <--> 2CO(g) K2 = ?

19. MORE ABOUT K!!!! • When adding reactions to produce a net equation, ________ K values. • For a 2 reactions, with K1 and K2, Knet = K1K2