1. Chemical Equilibrium Chemistry, The Central Science, 10th edition
Theodore L. Brown; H. Eugene LeMay, Jr.;
and Bruce E. Bursten
Chemical Equilibrium
Troy Wood
University of Buffalo
Buffalo, NY
 2006, Prentice Hall

2. For the gas-phase reaction A B
the forward reaction rate is 3.0  104 s1 and the reverse reaction rate is 1.5  102 s1. What is the value of the equilibrium constant, Keq?
0.02 50
0.0004
2500

3. Correct Answer:
0.02 50
0.0004
2500

4. Does the following reaction represent a homogenous or a heterogenous equilbrium?
C(s) + CO2(g) CO(g)
Homogenous
Heterogeneous

5. Correct Answer: Homogenous Heterogeneous
This is definitely a heterogeneous equilibrium because the reactants and products exist in two different phases, the solid and gaseous states.

6. 2 Ag(s) + Zn2+(aq) 2 Ag+(aq) + Zn(s)
Which of the following is the correct Keq for the equilibrium equation below?
2 Ag(s) + Zn2+(aq) Ag+(aq) + Zn(s)

7. Correct Answer: [2Ag+][Zn] Keq = ___________ [2Ag][Zn2+] [Zn2+]

8. Correct Answer (cont.):
Remember the equilibrium constant expression is given in terms of concentrations of products (raised to the exponent of their coefficients) divided by concentrations of reactants (raised to the exponent of their coefficients). Pure solids, liquids, and solvents are not included in the expression.

9. [ ] K B A D C = b a d c eq For the following hypothetical reaction:
2 Y(aq) + 3 Z(aq) A(aq)
Calculate Keq given the following equilibrium concentrations: [A] = 0.50 M, [Y] = 0.10 M, [Z] = 1.0 M [ ] b a d c eq K B A D C =
2.5
5.0
0.40
0.025
50.

10. [ ] [ ] [ ] Correct Answer: 0.50 K = 0.10 1.0 2.5 5.0 0.40 0.025 50.eq [ ] 2 [ ] 3
0.10
1.0

11. For the following hypothetical reaction: 2 X(g) + Y(g) A(g)
Keq = At a point during the reaction, the concentrations are [A] = 1.0 M, [X] = 0.50 M, and [Y] = 0.10 M. How will the reaction proceed to achieve equilibrium?
From left to right (toward products)
From right to left (toward reactants)
Already at equilibrium

12. [ ] [ ] [ ] Correct Answer: 1.0 K = 0.50 0.10
From left to right (toward products)
From right to left (toward reactants)
Already at equilibrium [ ]
1.0 K = [ ] [ ] c 2
0.50
0.10
Because Kc < Keq, the reaction will shift from reactants toward products to achieve equilibrium.

13. Y(g) + Z(g) 2 A(g) 4 A(g) 2 Y(g) + 2 Z(g)
For the following hypothetical reaction:
Y(g) + Z(g) A(g)
Keq = 4.0  102. Given that, what is the value of Keq for the reaction:
4 A(g) Y(g) + 2 Z(g) 25
5.0
0.016
6.3  102

14. Correct Answer: 25
5.0
0.016
6.3  102
The second equation is twice the first and reversed. Thus, Keq of the second equation is related to the first as shown below:

15. The following reaction is at equilibrium: N2(g) + 3 H2(g) 2 NH3(g)
If we remove NH3(g), in what direction will the reaction move to reestablish equilibrium?
From left to right (toward products)
From right to left (toward reactants)
No change in equilibrium

16. Correct Answer: From left to right (toward products)
From right to left (toward reactants)
No change in equilibrium
If [NH3] is decreased, to return to equilibrium, more NH3 must be produced from the reactants. Thus, the reaction shifts from the reactants to the products.

17. The following reaction is at equilibrium: N2(g) + 3 H2(g) 2 NH3(g)
If we increase the volume while holding the temperature constant, in what direction will the reaction move to reestablish equilibrium?
From left to right (toward products)
From right to left (toward reactants)
No change in equilibrium

18. Correct Answer: From left to right (toward products)
From right to left (toward reactants)
No change in equilibrium
Increasing the volume causes a shift in the equilibrium in the direction that produces more gas molecules, in this case on the reactants side.

19. The following reaction is at equilibrium: N2(g) + O2(g) 2 NO(g)
If we increase the pressure, in what direction will the reaction move to reestablish equilibrium?
From left to right (toward products)
From right to left (toward reactants)
No change in equilibrium

20. Correct Answer: From left to right (toward products)
From right to left (toward reactants)
No change in equilibrium
The number of gas molecules on both sides of the equation are equal; thus, changing the pressure will not change the equilibrium position.

21. The following reaction is at equilibrium: N2(g) + O2(g) 2 NO(g)
DH° = kJ. In what direction will the reaction move to reestablish equilibrium if the temperature is decreased?
From left to right (toward products)
From right to left (toward reactants)
No change in equilibrium

22. Correct Answer: From left to right (toward products)
From right to left (toward reactants)
No change in equilibrium
As the temperature is lowered, equilibrium will shift to the side of the equation that produces heat. Thus, for an endothermic reaction, the equilibrium shifts from right to left toward the reactants.