Marquez
AP Chemistry
Equilibrium Review
A. Equilibrium/Le Chatelier’s Simulations.
All Reactions are reversible. As a consequence, every reaction system will eventually reach a point where the
concentrations of the reactants and products no longer change. This is known as the equilibrium position. If a stress is
applied to the system, the system will adjust in such a way to address the stress that has been applied.
Go to http://www.cpp.edu/~jiselco/dynamicequilibrium/ and click on the Le Chatelier tab.
1. Under the A→B select 20% and under B→A select 40%.
a. Prediction: At equilibrium, what species (A or B) will be in greatest concentration:__________________
b. Will the value of K be greater than or less than 1?:___________________
c. Using the simulations, fill in the columns under A →B and B→A. The chosen percentage represents that
amount of reactant and product that will be converted. Only the correct value will be accepted. As you
complete the simulations table, fill in the table above and sketch out the produced graph.
i. When Equilibrium is reached, what is the K value for this system? Was your prediction correct?
_____________________
ii. Once your reach equilibrium, create a stress! Change the equilibrium concentration of A by 20
while keeping the B concentration the same.
1. Continue filling in the table until you reach equilibrium. Continue to fill the table above
with the new values. Additional, continue the produced sketch above, showing the
addition of the A.
2. Once equilibrium is reached, determine the equilibrium constant. Are you surprised
with your calculated value? Explain._______________________________________
_____________________________________________________________________
_____________________________________________________________________
Marquez
AP Chemistry
d. Design an experiment where, at equilibrium, the concentration of product will be greater than the
concentration of the reactant.
i. A%= ________________
ii. B%= _______________
iii. Value of K: _______________
iv. Show your experiment by feeling in the table below and sketching out the graph that was
produced.
2. Under what conditions can you produce a K value of 1? ____________________________________________.
3. Design an experiment that reaches equilibrium and then gets “stressed” twice.
a. How long did it take for the last stress to equilibrate? __________________________
b. Show the graph produced below:
Marquez
AP Chemistry
Calculations
4. Write equilibrium expressions for Kc, and for Kp, if applicable, for the following processes:
a. 2CO2(g)  2CO(g) + O2(g)
b. H2O(g) + C(s)  CO(g) + H2(g)
c. HCOOH(aq)  H+(aq) + HCOO-(aq)
d. 2HgO(s)  2Hg(l) + O2(g)
5. The following equilibrium constants were determined at 1123 K:
C(s) + CO2(g)  2CO(g)
Kp` =1.3x1014
CO(g) + Cl2(g)  COCl2(g)
Kp`` =6.0x10-3
Write the equilibrium constant expression Kp, and calculate the equilibrium constant at 1123 K for
C(s) + CO2(g) + 2Cl2(g)  2COCl2(g)
6. At a certain temperature the following reactions have the constant shown:
S(s) + O2(g) ↔ SO2(g)
Kp` = 4.2x1052
2S(s) + 3O2(g) ↔ 2SO3(g)
Kp``= 9.8x10128
Calculate the equilibrium constant Kc for the following reaction at that temperature:
2SO2(g) + O2(g) ↔ 2SO3(g)
Marquez
AP Chemistry
7. Consider the following reaction at equilibrium:
A(g)  2B(g)
From the data shown here, calculate the equilibrium constant (both Kp and Kc) at each temperature.
Temperature (°C)
200
300
400
[A] (M)
[B] (M)
0.0125
0.171
0.250
0.843
0.764
0.724
Is it endothermic or exothermic? Jusitfy your answer.
8. The equilibrium constant Kc for the reaction
H2(g) + I2(g)  2HI(g)
Is 54.3 at 430°C. At the start of the reaction there are 0.714 mole of H2, 0.984 mole of I2, and 0.886 mole of HI in
a 2.40 L reaction chamber. Calculate the concentration of the gases at equilibrium.
9. Consider the following equilibrium reaction in a closed container:
Heat+ CaCO3(s)  CaO(s) + CO2(g)
Which will be favored, Reactants or Products, if …..
(a) the volume is increased
_________________________________
(b) some CaO is added to the mixture
_________________________________
(c) some CaCO3 is removed
_________________________________
(d) some CO2 is added to the mixture
_________________________________
(e) a few drops of a NaOH solution are added to the mixture
(g) temperature is increased.
__________________________
_________________________________
Marquez
AP Chemistry
10. When heated, ammonium caramate decomposes as follows:
NH4CO2NH2(s) ↔ 2NH3(g) + CO2(g)
At a certain temperature the equilibrium pressure of the system is 0.318 atm. Calculate the Kp for the reaction.
11. Consider the equilibrium
2NOBr(g) ↔ 2NO(g) + Br2(g)
If nitrosyl bromide is 34 % dissociated at 25 °C and the total pressure is 0.25 atm, calculate the Kp and Kc for the
dissociation at this temperature.
12. Consider the following reaction, which takes place in a single elementary step:
k1
2A + B ↔ A2B
k-1
If the equilibrium constant Kc is 12.6 at a certain temperature and if k-1 = 5.1x10-2s-1, calculate the value of k1.
(Hint: Write the expression for Kc and the kinetic expression for a fast equilibrium for the reaction. Look for a
way to algebraically connect both of this expressions.)
Marquez
AP Chemistry
13. A mixture of 0.500 mol H2 and 0.500 mol I2 was placed in a 1.00 L stainless steel flask at 400 °C. The equilibrium
constant Kc for the reaction
H2(g) + I2(g) ↔ 2HI(g)
is 54.3 at this temperature.
a. Calculate the concentration of H2, I2, and HI at equilibrium.
b. Suppose that the initial concentration of H2, I2, and HI are 0.00623 M, 0.00414, and 0.0224 M, respectively.
Calculate the concentrations of these species at equilibrium. (Hint: you need to show quadratic work.)
Marquez
AP Chemistry
Free Response:
C(s) + CO2(g) ↔ 2CO(g)
1. Solid carbon and carbon dioxide gas at 1160 K were placed in a rigid 2.00 L container, and the reaction
represented above occurred. As the reaction proceeded, the total pressure in the container was monitored.
When equilibrium was reached, there was still some C(s) remaining in the container. Results are recorded in the
table below.
Time
Total Pressure of Gases
(hours)
in Container at 1160 K
(atm)
0.0
5.00
2.0
6.26
4.0
7.09
6.0
7.75
8.0
8.37
10.0
8.37
a. Write the expression for the equilibrium constant, Kp, for the reaction
b. Calculate the number of moles of CO2(g) initially placed in the container. (Assume that the volume of
the solid carbon is negligible.)
c. For the reaction mixture at equilibrium at 1160 K, the partial pressure of the CO2 (g) is 1.63 atm.
Calculate the
i. Partial pressure of CO(g)
ii. Value of the equilibrium constant Kp.
d. If a suitable solid catalyst were placed int eh reaction vessel, would the final total pressure of the gases
at equilibrium be greater than, less than, or equal to the final pressure of the gases at equilibrium
without the catalyst? Justify your answer.
In another experiment involving the same reaction, a rigid 2.00 L container initially contains 10.0 g of
C(s), plus CO(g) and CO2(g), each at a partial pressure of 2.00 atm at 1160 K.
e. Predict whether the partial pressure of CO2(g) will increase, decrease, or remain the same as this system
approaches equilibrium. Justify your prediction with a calculation.
Marquez
AP Chemistry
2. Hydrogen gas reacts with solid sulfur to produce hydrogen sulfide gas.
H2(g) + S(s) ↔ H2S (g)
ΔHrxn = -20.17 kJ/mol
An Amount of solid S and an amount of gaseous H2 are placed in an evacuated container at 25 °C. At
equilibrium, some solid S remains in the container.
Predict an explain each of the following. In each case, predict what the state change will have on the relative
values of K and Q
a.
the effect on the equilibrium partial pressure of H2S gas when additional solid sulfur is introduced into the
container.
b. the effect on the equilibrium partial pressure of H2 gas when additional H2S gas is introduced into the
container.
c. the effect on the mass of solid sulfur present when the volume of the container is increased
d. the effect on the mass of solid sulfur present when the temperature is decreased
e. the effect of adding a catalyst to initial amount of reactants.