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To get equilibrium handouts, click HERE.
Here are some typical exam questions concerning equilibrium.
| 1. Write the equilibrium constant
expressions, Kc or Kp, for the following systems: |
| (a) 2NO(g) + 2CO(g)
<=====> N2(g) + 2CO2(g) |
Kc = [N2][CO2]2
/ [NO]2[CO]2 |
| (b) 2NH3(g)
+ CO2(g) <=====> NH2COONH4(s) |
| Kc = 1 / [NH3]2[CO2] |
| 2. One mol (1.00 mol) of PCl5 is
placed in a 10.0 L flask and allowed to come to equilibrium at 250oC. At
equilibrium, 0.470 mol of Cl2 is present. Calculate Kc for: PCl5(g) <=====>
PCl3(g) + Cl2(g) |
Kc = 0.042 |
| 3. Consider the following equilibrium 2 H2S(g) + 3 O2(g)
<=====> 2 SO2(g) + 2 H2O(g)
in which 0.50 mol of SO2 and 1.0 mol of H2O
are placed in a 5.0 L vessel and allowed to come to equilibrium. Write the equilibrium
concentration expressions for dioxygen, O2, and sulfur dioxide, SO2.
Use "x" in units of mol, not molarity. |
[O2]eqm
= [3x/5]
[SO2]eqm = [(.50-2x)/5] |
| 4. Sulfuryl chloride, SO2Cl2,
decomposes at 50oC as shown below. Kc at 50oC is 0.120 SO2Cl2(g)
<===> SO2(g) + Cl2(g)
0.800 mol of SO2Cl2 is placed in a
2.00 L container maintained at 50oC, and is allowed to come to equilibrium with
SO2 and Cl2. |
| (a) Calculate the molarity of SO2Cl2
and the number of mol of Cl2 present at equilibrium. [SO2Cl2]eqm = 0.233M
Cl2 = 0.33 mol |
| (b) What is the %-dissociation of SO2Cl2
at equilibrium? %-diss = 42% |
| (c) If you started with 0.10 mol of SO2Cl2,
0.10 mol of SO2 and 0.20 mol of Cl2 in the 2.00 L vessel at 50oC,
in which direction would the mixture move to reach equilibrium? Prove your answer with the
appropriate calculation. move right, move left, not move |
| 5. Carbon monoxide reduces nickel oxide to
nickel metal: CO(g) + NiO(s)
<===> CO2(g) + Ni(s)
The value of Kp for this reduction falls from
4540 at 936 K to 1580 at 1125 K. Predict the effect of each of the following on the
equilibrium yield of nickel metal:
The mass of Ni metal at eqm will: (note:
mass not concentration) |
| (a) reducing the volume of the container:
increase / decrease / not change |
| (b) increasing the temperature: increase / decrease / not change |
| (c) increasing the concentration of CO2:
increase / decrease / not change |
| (d) adding more NiO to the reaction vessel:
increase / decrease / not change |
| (e) increasing the concentration of CO: increase / decrease / not change |
| (f) adding a catalyst to the reaction:
increase / decrease / not change |
| (g) burning incense and chanting: increase /
decrease / not change |
| 6. Carbon monoxide, CO, and hydrogen,H2,
can react to produce methyl alcohol, CH3OH, quickly attaining equilibrium in a
closed container. CO(g) + 2
H2(g) <===> CH3OH(g)
delta Hrxn = 18 kJ
List four things you could do to increase the equilibrium
molarity of CH3OH: |
| 1. inc. T
3. Inc [CO] |
| 2. dec V
4. Inc [H2] |
| 7. At 25C, Kc = 0.145 for the
following reaction in the solvent CCl4. 2 BrCl <===> Br2 +
Cl2
If the initial concentrations of Br2 and Cl2
are each 0.450 M in a solution initially containing no BrCl, what will their equilibrium
concentrations be? |
[Br2]eqm
= 0.205 M [Cl2]eqm
= 0.205 M |
| 8. Consider this equation:
C2H2(g) + 5 N2O(g)
<===> 2 CO2(g) + H2O(g) + 5 N2(g) Assume you placed 0.50 mol of each component except N2O
in a 15 L container and allowed the mixture to reach equilibrium. Write the expressions
for the concentration of N2O and CO2 once equilibrium is attained.
Don't calculate the actual concentration, just write the expressions that contain the
"x" terms. |
[N2O]eqm
= [5x/15]
[CO2]eqm = [(.50-2x)/15]
"x" is in moles |
| 9. (a) Consider the following equilibrium: NO2(g) + NO(g)
<===> N2O3(g)
At a particular temperature, Kc for this
reaction was measured to be 2.50. At this temperature 1.00 mol of NO2 and 0.700
mol of NO were placed in a 4.00 L vessel and allowed to come to equilibrium. What number
of mol of N2O3 would be present at equilibrium?
mol of N2O3 = 0.23 mol |
| (b) In the same system as that described in
part (b), what would be the molarity of NO2 once equilibrium is attained? [NO2]eqm = 0.19 M |
| 10. A 1.00 mol sample of HI was
placed in a 10 L vessel at 460C, and the reaction system was allowed to come to
equilibrium. At equilibrium, 0.11 mol of H2 and 0.11 mol of I2 were
present in the container. What is Kc for the following reaction at this
temperature? H2(g) + I2(g)
<===> 2 HI(g) |
| a. 0.020 |
c. 8.1 |
| b. 7.1 |
d. 50 |
| 11. If the system NH4Cl(s)
<====> NH3(g) + HCl(g) is at equilibrium at
constant temperature, and more NH4Cl is added doubling the number of mol of NH4Cl
in the vessel, then: |
| a. The mass of NH3 and HCl doubles
in the container. |
c. The partial pressures of both NH3
and HCl increase until equilibrium is attained. |
| b. The equilibrium concentrations of NH3
and HCl increase. |
d. The partial pressures of
NH3 and HCl in the vessel remain unchanged. |
| 12. Dinitrogentetroxide readily
undergoes decomposition to form red-brown NO2: N2O4(g) <===> 2 NO2(g)
At 25oC, 0.11 mol N2O4
reacts to form 0.10 mol N2O4 and 0.02 mol NO2.
At 90oC, 0.11 mol N2O4 reacts to form 0.05 mol N2O4
and 0.12 mol NO2. From these data we can conclude that: |
| a. N2O4 reacts by a
first-order rate law. |
c. N2O4 molecules react
faster at 25oC than at 90oC. |
| b. The forward reaction is exothermic. |
d. Kc for the
reaction increases with increasing temperature. |
| 13. Kc = 4.0 at 500oC
for: CO(g) + H2O(g)
<===> CO2(g) + H2(g) 0.10 mol of CO, 0.10 mol of H2O, 0.25 mol of CO2 and 0.25
mol of H2 were placed in a 10 liter vessel at 500oC. In which
direction will the mixture move to achieve equilibrium? |
| a. to the right |
c. neither direction, it is already at
equilibrium |
| b. to the left |
d. Insufficient data are given to determine
the answer to this question. |
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