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Equilibrium Constants

Explore the principles of chemical equilibrium through the concepts of equilibrium constants Kc and Kp, which relate concentrations and partial pressures of reactants and products. Learn to write equilibrium expressions for various reactions, and understand how to calculate Kc and Kp from given concentrations or pressures at specific temperatures. The guide includes worked examples, such as the Haber process and shifts in equilibrium based on the reaction quotient (Qc and Qp). Perfect for students striving to master equilibrium concepts in chemistry.

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Equilibrium Constants

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  1. Equilibrium Constants Kc: concentration, M Kp: pressure, atm

  2. Equilibrium Expressions aA + bB  cC + dD Kc = [C]c[D]dKp = (PC)c(PD)d [A]a[B]b (PA)a(PB)b Kp = Kc(RT)Dn Dn= S gas product coefficients – S gas reactant coefficients *If the substance is a solid or a liquid, put a 1 in its place.

  3. Example #1 • Write the equilibrium expressions for Kc for the following. • 2H2O(l) 2H2(g) + O2(g) • 2HCl(aq)  H2(g) + Cl2(g)

  4. Example Problem #2 • The following equilibrium concentrations were observed for the Haber process at 127oC N2(g) + 3H2(g) 2NH3 (g) [NH3] = 0.031M [N2] = 0.85M [H2] = 0.0031M Calculate Kc and Kp.

  5. Example Problem #3 • The reaction below occurs at 25oC. 2NO(g) + Cl2(g) 2NOCl(g) The equilibrium partial pressures are: PNOCl = 1.2atm PNO = 0.05atm PCl2 = 0.30atm Calculate Kp and Kc.

  6. Reaction Quotient • Predicting shifts in equilibrium mathematically Qc = [C]c[D]dQp = (PC)c(PD)d [A]a[B]b (PA)a(PB)b Q<K: shifts right Q>K: shifts left Q=K: at equilibrium

  7. Example Problem #4 • The equilibrium constant, Kp, is 2.33 for the reaction C(s) + CO2(g) 2CO(g) at 50oC. If 0.75g of C, 3.5atm of CO2 and 4.5 atm CO are present in a container, is the reaction at equilibrium? If not, which way will it shift?

  8. Example #5 The equilibrium constant, Kp, for the reaction 2H2O(l) 2H2(g) + O2(g) is 5 x 10-6. If 50g of hydrogen, 25g of oxygen and 100g of water are placed in a 5L flask at 100oC, will the reaction be at equilibrium? If not, which way will it shift?

  9. Example #6 Consider the reaction: N2(g) + 3H2(g) 2NH3 (g) The equilibrium constant, Kc, at 25oC is 0.082. If 0.4mol of nitrogen, 0.098mol of hydrogen and 2.32mol of ammonia are present in a 4L container, is the system at equilibrium? If not, which way will it shift?

  10. Determining Equilibrium concentrations • The ICE method aA + bB  cC + dD I # # 0 0 C -ax -bx +cx +dx E #-ax #-bx cx dx I= initial concentrations, C= change during reaction process E = equilibrium concentrations.

  11. Example Problem #7 • For the reaction N2O4(g) 2NO2(g) the equilibrium constant, Kp, is 0.133. If 2.71 atm of N2O4 are introduced into a container, what will the equilibrium partial pressure be for all the species in the reaction?

  12. Example Problem #8 • For the reaction: CO(g) +H2O(g) CO2(g) + H2 (g) the equilibrium constant, Kc, is 5.10 at 700K. If 3 moles of CO and 3 moles of H2O are introduced into a 5L flask, what will the equilibrium concentrations be for all the species present in the reaction?

  13. Example #9 • For the reaction 2NOCl(g) 2NO(g) + Cl2(g) the equilibrium constant, Kc, is 1.6 x 10-5 at 35oC. If 3 moles of NOCl are placed in a 6L container, what will the concentrations of all the species reach at equilibrium?

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