Predicting if a Reaction is in Equilibrium Trial Keq Lesson 9 The Keq is a constant- a number that does not change Changing the volume, pressure, or any concentration, does not change the Keq. Only temperature changes the Keq Increasing a [Reactant] shifts right and maintains the Keq Increasing the temperature of an endothermic equilibrium shifts right and increases the Keq Ktrial How can you tell if a system is in equilibrium or not? Calculate a trial Keq. Use initial concentrations in the equilibrium expression- evaluate. How can you tell if a system is in equilibrium or not? Calculate a trial Keq. Put initial concentrations into the equilibrium expression and evaluate. If Kt < Keq Shifts right Kt If Kt = Keq If Kt > equilibrium Shifts left Kt Kt Keq 5 20 35 Keq 1. 10.0 moles of NH3, 15.0 moles of N2, and 10.0 moles of H2 are put in a 5.0 L container. Is the system in equilibrium and how will it shift if it is not? ⇄ 2NH3(g) 2.0 M N2(g) + 3H2(g) 3.0 M Kt = [N2][H2]3 [NH3]2 Kt < Keq Keq = 10 2.0 M = (3)(2)3 (2)2 Not in equilibrium Shifts right! = 6 2. 4.56 x 10-5 moles of NH3, 5.62 x 10-4 moles of N2, and 2.66 x 10-2 moles of H2 are put in a 500.0 mL container. Is the system in equilibrium and how will it shift if it is not? ⇄ 2NH3(g) 9.12 x 10-5 M Kt N2(g) + 3H2(g) 1.124 x 10-5 M = [N2][H2]3 [NH3]2 Kt > Keq = Keq = 10 5.32 x 10-2 M (1.124 x 10-3 )(5.32 x 10-2 )3 (9.12 x 10-5 )2 Not in equilibrium Shifts left! = 20.3 4. If 4.00 moles of CO, 4.00 moles H2O, 6.00 moles CO2, and 6.00 moles H2 are placed in a 2.00 L container at 670 oC. CO(g) + 2.00 M +x H2O(g) ⇄ 2.00 M +x 2.00 + x 2.00 + x CO2(g) 3.00 M -x 3.00 - x + H2(g) 3.00 M -x Keq = 1.0 Is the system at equilibrium? Kt = (3)(3) (2)(2) = 2.25 3.00 - x Not in equilibrium Keq = [CO2][O2] Shifts left! [CO][H2O] Calculate all equilibrium concentrations. (3 - x)2 = 2 (2 + x) 3 - x 2 +x = 1.0 1.0 3 - x = 2 + x 1 = 2x x = 0.50 M [CO2] = [H2] = 3.00 - 0.50 = 2.50 M [CO] = [H2O] = 2.00 + 0.50 = 2.50 M Size of the Keq Big Keq products Keq = reactants Keq = 10 Little Keq products Keq = reactants Keq = 0.1 Note that the keq cannot be a negative number! Keq = 1 products Keq = reactants