| Name _______________________________________ | Gen Chem II Lecture |
| Exam 4 | 24APR98 | Dr. L. J. Rivela |
| 1. YOU MUST
SHOW ALL EQUATIONS, LOGIC, AND CALCULATIONS IN ORDER TO RECEIVE
ANY CREDIT ! 2. ALL NUMERICAL ANSWERS MUST HAVE THE PROPER NUMBER OF SIGNIFICANT FIGURES AND BE EXPRESSED IN SCIENTIFIC NOTATION WHERE NECESSARY. |
| 1. | A chemical substance, A, is found to follow zero order kinetics, i.e. rate = k[A]0. Experimental data indicates that it takes 678 seconds for the molar concentration of A to decrease from 3.25 to 0.00893. Calculate the value of the rate constant and the half-life for this zero order process. [12] |
| 2. | On the coordinates provided, sketch a potential energy hill diagram for an endothermic reaction. Completely label the diagram. [8] |
| 3. | Write the equilibrium constant expressions, Kc, for the following reactions . . . . |
| [a] CS2(g) + 4 H2(g) = CH4(g) + 2 H2S(l) | |
| [4] | [b] 2 NaHCO3(s) Na2CO3(s) + H2O(g) + CO2(g) |
| 4. | On the coordinates provided, sketch a well-labeled diagram to illustrate how temperature influences the rate of a chemical reaction. [8] |
| 5. |
The equilibrium constant for the reaction N2O2(g) = N2(g) + O2(g) ; is 0.456 at 322 K. What is the value of Kc for the following reaction at 322 K ? [4] 3 N2O2(g) = 3 N2(g) +3 O2(g) |
| 6. |
Consider the reaction : 4 Cl2(g) + 4 H2O(g) = 8 HCl(g) +2 O2(g) 0.42 mole of Cl2 and 0.56 mole of H2O(g) were sealed in a 2.00 liter vessel. When equilibrium was established, the flask was found to contain 0.160 mol of HCl. On the basis of this data calculate Kc. [10] |
| 7. |
Monoatomic chlorine will dimerize at 25°C : 2 Cl(g) = Cl2(g); Kc for this reaction is 3.80 at 25°C. If one places 0.400 mol of Cl in a 500 mL container at 25°C and the system attains equilibrium, calculate the concentration of Cl2 at equilibrium. [12] |
| 8. | Predict the direction of reaction for each of the following chemical systems at equilibrium, when the system undergoes the indicated change of condition (stress) [15] |
|
System |
Stress |
Change |
||
| [a] |
2 Cl2(g) + 2 H2O(g) = 4 HCl(l) + O2(g); |
H2O(g) is added |
= O - |
|
| [b] |
PCl5(g) = PCl3(g) + Cl2(l); |
Volume decreases |
= O - |
|
| [c] |
H2(g) + I2(g) = 2 HI(g) |
Pressure decrease |
= O - |
|
| [d] |
NH4Cl(s) = NH3(g) + HCl(g); |
NH4Cl(s) is added |
= O - |
|
| [e] |
N2O4(g) = 2 NO2(g) : delta H = 30 kJ/mol; |
Temperature increase |
= O - |
| 9. | Calculate the [H+], [OH-], pH, of a solution that has a pOH of 11.45. [12] |
| 10. | Aniline, C6H5NH2, is a weak base. [a] The conjugate acid of Aniline is _______________________ [b] write the hydrolysis reaction of aniline. [4] |
| 11. | Calculate the percentage ionization of a 0.10 M HOBr (hypobromous acid solution). [10] |
| 12. | Calculate the pH of a 0.60 M NaF [sodium fluoride] solution. [12] |
| 13. |
Amphoterism is a characteristic which is exhibited by many substances. [7] [a] define amphoterism . . . . . |
| 14. | What is the difference between a strong acid and a weak acid? [2] |
| 15. | 100 mL of 0.25 M HNO3 is mixed with 50 mL of 0.50 M KOH. Assuming that the volumes are additive, what is the pH of the resulting solution ? [10] |
| 16. | Please clearly DEFINE
the following terms with short concise
statements. [9] [a] Lewis Base [b] Arrhenius Base [c] Bronsted-Lowry Acid |
| 17. |
A buffer is prepared by mixing 3.00 mol of HC2H3O2 and 4.00 mol of NaC2H3O2 in enough water to form 5.00 liters. [20] [a] Calculate the pH of this buffer solution. [b] Calculate the pH of the solution that results adding 0.40 mol of NaOH to 2.00 liters of the BUFFER. |
| Extra Credit . . . if you like |
|
A chemist performs the following serial aqueous dilutions : [12] 10.0 mL of 1.0 x 10-3 M KOH was diluted to 1000
mL [Solution A] Determine the pH of Solution A SHOW YOUR LOGIC AND WORK AND COMMENT ON THE RESULTING VALUES. |
|
~ Total points = 159 points ~ |