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 If Kt = Keq If Kt > Keq Shifts right equilibrium Shifts left Kt Kt Kt Keq 5 20 35

1. 10. 0 moles of NH3, 15. 0 moles of N2, and 10 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) ⇄ N2(g) + 3H2(g) Keq = 10 2.0 M 3.0 M 2.0 M [N2][H2]3 Kt = = (3)(2)3 = 6 (2)2 [NH3]2 Kt < Keq Not in equilibrium Shifts right!

2. 4. 56 x 10-5 moles of NH3, 5. 62 x 10-4 moles of N2, and 2 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) ⇄ N2(g) + 3H2(g) Keq = 10 9.12 x 10-5 M 1.124 x 10-5 M 5.32 x 10-2 M [N2][H2]3 Kt = = (1.124 x 10-3 )(5.32 x 10-2 )3 = 20.3 (9.12 x 10-5 )2 [NH3]2 Kt > Keq Not in equilibrium Shifts left!

4. If 4. 00 moles of CO, 4. 00 moles H2O, 6. 00 moles CO2, and 6 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) + H2O(g) ⇄ CO2(g) + H2(g) Keq = 1.0 2.00 M 2.00 M 3.00 M 3.00 M Is the system at equilibrium? +x +x -x -x (3)(3) Kt = = 2.25 (2)(2) 2.00 + x 2.00 + x 3.00 - x 3.00 - x Not in equilibrium Shifts left! [CO2][O2] Keq = [CO][H2O] Calculate all equilibrium concentrations.

(3 - x)2 = 1.0 (2 + x)2 3 - x = 1.0 2 + x 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

reactants Little Keq Keq = Keq = 0.1 products Keq = reactants Keq = 0.1 Note that the keq cannot be a negative number!

Keq = 1 products Keq = reactants