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Chemical Equilibrium Q, K, and Calculations Chapter 16

Chemical Equilibrium Q, K, and Calculations Chapter 16. 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).

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Chemical Equilibrium Q, K, and Calculations Chapter 16

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  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

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