Predicting if a Reaction is in Equilibrium Trial Keq Lesson 9
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Transcript of Predicting if a Reaction is in Equilibrium Trial Keq Lesson 9
Predicting if a Reaction is in Equilibrium
Trial Keq
Lesson 9
The Keq is a constant- a number that does not change
Increasing the temperature of an endothermic equilibrium shifts right and increases the Keq
Increasing a [Reactant] shifts right and maintains the Keq
Only temperature changes the Keq
Changing the volume, pressure, or any concentration, does not change 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.
Keq
Kt
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
equilibrium
If Kt > Keq
Kt Kt
If Kt < Keq
Shifts right Shifts left
5 20 35
Shifts right!
2NH3(g) ⇄ N2(g) + 3H2(g) Keq = 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?
2.0 M 3.0 M 2.0 M
Kt = [N2][H2]3
[NH3]2
= (3)(2)3 = 6(2)2
Not in equilibriumKt < Keq
Shifts left!
2NH3(g) ⇄ N2(g) + 3H2(g) Keq = 10
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?
9.12 x 10-5 M 1.124 x 10-5 M 5.32 x 10-2 M
Kt = [N2][H2]3
[NH3]2
= (1.124 x 10-3 )(5.32 x 10-2 )3 = 20.3(9.12 x 10-5 )2
Not in equilibriumKt > Keq
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
Is the system at equilibrium?
Calculate all equilibrium concentrations.
Shifts left!
Not in equilibrium
Kt =(3)(3)(2)(2)
= 2.25+x +x -x -x
2.00 M 2.00 M 3.00 M 3.00 M
2.00 + x 2.00 + x 3.00 - x 3.00 - x
Keq =[CO2][O2]
[CO][H2O]
(3 - x)2 (2 + x)2
= 1.0
= 1.03 - x 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
products
reactants
Keq =
Big Keq
Keq = 10
reactants
products
Keq =
Little Keq
Keq = 0.1
Note that the keq cannot be a negative number!
Keq = 1
Keq =
products
reactants