Chemistry 1212
Practice Final Exam Problems
I have gone through my files and selected several old final exam problems for you to use as practice problems for the final. I have tried to select some of the more interesting problems that are integrated or require some extra thought.
By no means should you consider this a complete list of concepts or topics included on the final exam. There are many topics that do not occur here: phase diagrams, osmosis, etc. I simply cannot give you everything. Also, do not expect the problems on your exam to be the “same” as the ones listed here, these are only a small set of examples of problems that have gone before your time.
This should not be your only avenue of study for the final.
I have included the answers on the last page of this set. Good luck.
Feel free to use your textbook for electrode potentials, constants, etc. as you deem necessary.
1. An equilibrium mixture of SO2, SO3 and O2 gases is maintained in a 11.5 L flask at a temperature at which Kc = 55.2 for the reaction shown below. If the number of moles of SO3 in the flask at equilibrium is twice the number of moles of SO2, how much O2 is present in the flask at equilibrium? Show all work.
2 SO2 (g) + O2 (g) 2 SO3 (g)
2. What is the vapor pressure at 25 ºC of a solution of a non-volatile solute in benzene if the solution freezes at 2.63 ºC? The vapor pressure of pure benzene at 25 ºC is 93.4 torr and pure benzene freezes at 5.50 ºC. kfp (benzene) = 5.12; MW(benzene) = 78.
3. A 1.00 m solution of HF freezes at –1.90 ºC. Determine the Ka for HF at –1.90 ºC. Show all work. kfp(water) = 1.86 (Hint: you can assume m M.)
4. The equilibrium constant for the reaction below is 54.3 at 430 ºC. At the start of the reaction there are 0.714 mole of H2, 0.984 mole I2 and 0.886 mole of HI in a 2.40 liter reaction chamber. Calculate the concentrations of the gases at equilibrium. Show all work.
H2 (g) + I2 (g) 2 HI (g)
5. A solution is prepared by condensing 4.00 liters of a gas, measured at 27 ºC and 748 mm Hg pressure, into 58.0 g of benzene. Calculate the freezing point of this solution. (See problem #2 above for data.)
6. A galvanic cell consists of a silver electrode in contact with 346 ml of 0.100 M AgNO3 solution and a magnesium electrode in contact with 288 ml of 0.100 M Mg(NO3)2 solution. Calculate Ecell for the cell at 25 ºC. Show work.
Note: Ag+| Ag, E = +0.799v; Mg+2 | Mg, E = -2.357 v
7. Consider the reaction: X + Y Z The following data were obtained at 360 K.
[X] / [Y] / Initial rate of disappearance of X (moles/liter·sec)0.10 / 0.50 / 0.147
0.20 / 0.30 / 0.127
0.40 / 0.60 / 4.064
0.20 / 0.60 / 1.016
0.40 / 0.30 / 0.508
A. Determine the order of the reaction. Show work.
B. Determine the initial rate of disappearance of X when [X] and [Y] are 0.20 M and 0.30 M respectively. Show all work.
8. The rate constant of the second order reaction: 2 HI (g) → H2 (g) + I2 (g) is 2.4 x 10-6 L·mole·sec-1 at 575 K and 6.0 x 10-5 L·mole·sec-1 at 630 K. Calculate the activation energy of the reaction. Show all work.
9. You have concentrated ammonia (28.0% by wt.; D = 0.90 g/ml) and solid NH4Cl (MW = 53.5) in the lab. Assuming no volume change upon addition of solid, construct a buffer solution with pH = 10.00. Show all work. Kb(NH3) = 1.8 x 10-5
10. Consider: Ag+(aq) + Fe+2(aq) Ag (s) + Fe+3(aq)
If equal volumes of 1.0 M solutions of Ag+ and Fe+2 are mixed, what is the equilibrium concentration of Fe+2? Show all work. (Hint: you need to calculate a K value). Note: Ag+| Ag, E = +0.799v; Fe+3 | Fe+2, E = +0.769.
11. Consider the all gaseous reaction: A + 2 B C + D
A. If 8 moles of B are placed into a 1 liter flask with 5 moles of A, we find that at equilibrium, 75% of B is converted to product. What are [A], [B], [C], [D] and the K value at equilibrium? Show work.
B. Sufficient B is added to the mixture to increase the number of moles of C to 4 at equilibrium. How many moles of B must have been added? Show work.
C. If the total volume were increased to 2 liters, will the system still be at equilibrium? If not, how will it shift?
12. Consider the reaction: S2Cl4 (g) 2 SCl2 (g) K = 25.0
If 5.0 moles of SCl2 are in equilibrium with 1.0 mole of S2Cl4 in a 1.0 liter container. Suddenly, with no change in T, the volume of the container is decreased to 0.50 liter. Find the concentrations of SCl2 and S2Cl4 at the new equilibrium. Show work.
13. A proposed mechanism for the reaction: 2 NO (g) + O2 (g) NO2 (g) is:
NO + O2 NO3 (fast)
NO3 + NO 2 NO2 (slow)
Does the rate law derived from this mechanism agree with the experimentally determined rate law which is:
Rate = k [NO]2 [O2]
Answers:
1. 0.0725 M = 0.833 moles
2. 89.5 torr
3. 4.08 x 10-4
4. [H2] = 0.069; [I2] = 0.181; [HI] = 0.827
5. –8.61 ºC
6. 3.126 v
7. A. 5th B. 0.127 mole/liter·sec (See Experiment #2)
8. 176.2 kJ
9. 142.5 g NH4Cl per liter of NH3
10. 0.273 M
11. A. [A] = [B] = 2 M; [C] = [D] = 3 M; K = 1.125
B. 3.77 moles C. No, shifts left
12. [SCl2] = 8.38 M; [S2Cl4] = 2.81 M
13. Yes