Use your time wisely. Do not get stuck on one question. WORK MUST BE SHOWN CAREFULLY, WITH UNITS AT EVERY STEP OF SETUP.

Transcription

1 Spring 2014 CCBC-Catonsville (Wed 3/12/14) Use your time wisely. Do not get stuck on one question. WORK MUST BE SHOWN CAREFULLY, WITH UNITS AT EVERY STEP OF SETUP. PAGE TOTAL SCORE POSSIBLE YOUR SCORE TOTAL 100 Bonus p.5 5 Adjusted Exam Total = Current Course Average (based on Exams I & II, 6 quizzes, 9 Wiley HW, 2 paper HW) = Integrated Rate Laws R = J mol 1 K 1 R = atm L mol 1 K 1 zero: [A] = [A] o kt first: ln [A] = ln[a] o kt second: 1 1 kt [A] t [A] o SOLVENT FREEZING POINT ( C) k f ( C m 1 ) BOILING POINT ( C) k b ( C m 1 ) H 2 O acetic acid benzene (C 6 H 6 ) cyclohexane (C 6 H 12 ) carbon tetrachloride (CCl 4 )

2 Spring 2014 Page 1 Multiple Choice (4 pts each): Circle the one best answer for each of the following. 1. A compound containing the elements X and Y crystallizes in a cubic unit cell with Y at each corner of the cell and X in the center of each face. Based on this crystal structure, what should we expect the formula of this compound to be? A. X 2 Y 3 B. X 3 Y 2 C. XY 3 D. X 3 Y E. X 3 Y 4 2. Which represents a higher efficiency in packing? A. B. C. They are the same. 3. Which has the lower freezing point? A. 0.4 m NaCl B. 0.2 m NaCl C. They have the same boiling point 4. Which direction will the water flow? The two chambers are separated by a semipermeable membrane. 0.1 M NaCl 0.3 M NaCl A. Water will flow to the left. B. Water will flow to the right. 5. Which has the lower vapor pressure? A. 0.1 m Na 3 PO 4 B. 0.2 m NaCl C. They have about the same vapor pressure. 6. Which aqueous solution will have the highest freezing point temperature? A m MgBr 2 B m MgSO 4 C m KClO 3 D m MgCl 2 7. What happens to the van t Hoff factor as the concentration of a solution increases? A. It increases B. It decreases. C. It stays the same. 8. In order for a dissolution process of an ionic compound in water to be endothermic, which combination below must be true? A. The magnitude of the hydration energy must be greater than the magnitude of the lattice energy. B. The magnitude of the hydration energy must be less than the magnitude of the lattice energy. C. The magnitude of the hydration energy must equal to the magnitude of the lattice energy. 9. What happens to the solubility of a gas when the temperature is raised? A. It decreases. B. It increases C. It is not affected. 10. How is the half-life of a radioisotope affected by its concentration? A. It increases with concentration. B. It decreases with concentration C. It is unaffected by concentration.

3 Spring 2014 Page 2 Multiple Choice (4 pts each) continued: 11. For the reaction 2A + B Products, the rate equation was found to be rate = k[a] 2. If the rate constant was found to be M 1 min 1 and the reaction started with an initial concentration of A equal to 0.50 M, how long will it take for the concentration of A to reach 0.25 M? Ans. 12. For the reaction, 2R + 3S T + 3V, initial rate measurements were carried out and data for three runs are shown below: (You do not need to show me your work.) Experiment [R] [S] Rate (mol L 1 s 1 ) Based on the data, the rate law must be... A. Rate = k[r] 2 [S] 3 D. Rate = k[r][s] B. Rate = k[r][s] 2 E. Rate = k[r][s] 3 C. Rate = k[r] 2 [S] A reaction has the rate law, rate = k[a][b] 2. How will the rate change when the concentration of B is tripled while the concentration of A is kept constant? A. The rate will be doubled. B. The rate will be tripled. C. The rate will be quadrupled. D. The rate will not be affected. E. None of the above. 14. What would we have to plot on the y-axis in order to get a straight line for a reaction with this rate law? (The x-axis is time.) Rate = k[a] A. [A] B. 1/[A] C. ln [A] D. k 15. A reaction is first order overall. For a given sample, its initial rate is mol L 1 s 1 and 25.0 days later its rate dropped to 6.25x10 4 mol L 1 s 1. What is its half-life? A days B days C days D. 5.0 days E days

4 Spring 2014 Page (6 pts) In the graph below, make a sketch of the potential energy diagram of a reaction with an activation energy for the forward reaction of kj mol 1 and an enthalpy of reaction of 20.0 kj mol 1. Label the two axes. What is the activation energy for the reverse reaction? Circle one: A kj/mol B kj/mol C kj /mol D kj/mol E kj/mol 17. (10 pts) A) Draw the line whose slope would give us the instantaneous rate at 100 minutes. B) What would the sign of the slope be? Circle one: positive or negative C) What would the sign of the rate be? Circle one: positive or negative D) Is this a graph for the change in molarity of the reactant or product? Ans. E) What would the units of the slope be? Ans.

5 Spring 2014 Page (4 pts) For a reaction with Rate = k[a] 3 [B], what are the units of k? Ans. Show your work. Hint: What are the units of rate? 19. (10 pts) How many grams of benzoic acid (C 6 H 5 COOH) must be dissolved in g of carbon tetrachloride in order to give a solution that boils at 77.5 C? Show your work carefully. Units must be shown at every step of your calculation setup. Watch your sig. fig. Ans.

6 Spring 2014 Page (10 pts) Concentrated H 3 PO 4 has a density of g/cm 3 and is 85.5 % by mass. Calculate its molarity, molality and mole fraction in space shown below. SHOW YOUR WORK CAREFULLY WITH UNITS AT EVERY STEP. A. Calculate its molarity. Ans. B. Calculate its molality. Ans. C. Calculate the mole fraction of H 3 PO 4. Ans. BONUS POINTS: (1 pt) Make sure you have your full name on every page!!! (2 pt) Give the answer in the correct number of sig. fig. log 6.18x10 2 = x What is x? Ans. ln x = What is x? Ans. (2 pts) A reaction takes place only if the collisions of the reactants are effective collisions. Give two reasons why a collision might not be effective. Answer briefly but in COMPLETE SENTENCES. i) ii)