General Chemistry II ____________________

COOP VI (name)

 

1. Is the spontaneous melting of ice at room temperature an entropic driven or enthalpic driven reaction?

 

 

 

 

 

2. A reaction is always spontaneous if DH is __________(+ or -) and if DS is __________(+ or -).

 

 

 

 

3. Estimate the normal freezing pt. of HCl, given; DHofusion = 16.13 kJ/mol and ;

DSofusion = 85.77 J/mol-K.

 

 

 

 

 

4. Consider the decomposition of gaseous phosgene, COCl2 into gaseous chlorine and carbon monoxide. Using Standard thermodynamic tables in the back of your book:

 

a. What is the equilibrium constant at standard state conditions?

 

 

 

 

 

 

 

b. A what minimum temperature does this reaction become spontaneous?

 

 

 

 

 

 

5. State the First Law of Thermodynamics:

 

 

 

 

5. State the 2nd Law of Thermodynamics:

 

 

 

 

6. State the 3rd Law of Thermodynamics:

 

 

 

7. For each of the following, indicate if entropy of the system is increasing or decreasing.

 

a. CaCO3(s) --> CaO(s) + CO2(g)

 

 

b. 2CO(g) - 2C(s) + O2(g)

 

 

c. 2H2(g) + O2(g) --> 2H2O(l)

 

d. H2O(l) --> H2O(g)

 

 

e. 2Na(s) + H2O(l) --> 2NaOH(aq) + H2(g)

 

 

f. dissolving sodium chloride in water

 

 

g. sublimation of naphthalene

 

 

h. dissolving oxygen in water

 

 

i. boiling of alcohol

 

 

j. explosion of nitroglycerine

 

 

8. Calculate DSo for the following reaction at 25oC given that So at 25oC for O2(g), CO(g) and diamond are 205.0, 197.9 & 2.43 J/mol-K,

C(diamond) + O2(g) --> 2CO(g) respectively.

 

 

 

 

 

9. Consider the following reaction at 25oC.

 

C(s) + H2O(g) --> CO(g) + H2(g)

DGo = 91.2 kJ DSo = 135J/K

What is the value of DHo (kJ) for this reaction at 25oC?

 

 

 

 

 

 

 

10. When ammonium chloride dissolves in water the temperature of the solution is less than that of the original water sample. Thus, we know that DH is____and DS is____.

a. negative, positive b. negative, negative c. positive, positive

d. positive, negative e. negative, zero

 

 

 

 

11. A reaction that is not spontaneous at low temperature can become spontaneous at high temperature if DH is____and DS is____.

 

a. +,+ b. +,- c. -,- d. -,+ e. +,0

 

 

 

 

12. Which of the following is true about the equilibrium constant for a reaction if DG for the reaction is negative?

 

a. K=0 b. K=1 c. K>1 d. K<1 e. need more information

 

 

 

 

 

 

13. Consider the reaction NH3(g) + HCl(g) --> NH4Cl(s)

 

Determine the value of the equilibrium constant at 25o C and at 500 o C from the following thermodynamic data.

 

substance DHof DSo

NH3(g) -46.19 kJ/mol 192.5 J/mol-K

HCl(g) -92.30 186.69

NH4Cl(s) -314.4 94.6

 

13. Consider the electrolysis of NaCl. Write equations for the electrode reactions in each case and explain the difference, if any, between the products obtained by the two methods.

 

Molten NaCl

Anode: Cathode:

 

 

 

 

 

 

 

14. Distinguish between a voltaic and electrolytic cell.

 

 

 

 

15. Consider the oxidation of iron metal.

 

4Fe(s) + 3O2(g) 2Fe2O3(s)

 

 

a. From your personal experience in Arkansas, is this a spontaneous process?

 

 

 

b. From your knowledge of entropy, does the entropy of the reaction increase or decrease as the process proceeds?

 

 

 

c. It this an exothermic reaction?

 

 

 

d. What is the sign of the reduction potential for this reaction?

 

 

 

 

 

 

 

 

 

16. Consider the reaction between copper and iodine:

 

Cu(s) + I2(g) <== ==> Cu+2 + 2I- , K= 6.8x106

 

 

a. What is the anode half reaction?

 

 

b. What is the cathode half reaction?

 

 

 

c. Write the cell reaction in battery notation. Use a platinum wire for the iodide half cell electrode.

 

 

d. What is the standard emf for a copper/iodine cell?

 

 

 

e. What is the standard free energy for the copper/iodine cell?

 

 

 

 

f. What is the emf if the Iodine pressure is increased 10 fold in a cell initially at standard conditions?

 

 

 

 

17. What volume of oxygen gas is created at STP by the electrolysis of water after 185 seconds with a current of 0.0565 amps?

 

2H2O(l) O2(g) + 4H+(aq) + 4e-

 

 

 

 

 

 

18. Express the following reactions in standard electrochemical cell notation at standard state conditions:

 

a. Cd(s) + Sn+2(aq) Cd+2(aq) + Sn(s)

 

 

 

 

b. 2Al(s) + 3 Cd+2(aq) 2 Al+3(aq) + 3 Cd(s)

 

 

 

 

 

 

19. Using standard reduction potentials, determine if the following half reactions can occur at STP.

 

 

 

a. Oxidation of tin(II) by bomine

 

 

 

b. Reduction of nickle(II) by tin(II).

 

 

 

c. Oxidation of silver by lead(II)

 

 

 

d. Reduction of iodine by copper.

 

 

20. Consider a galvanic cell based on the reaction

 

2Fe+2(aq) + Cl2(g) 2Fe+3(aq) + 2Cl-(aq)

 

Calculate the cell potential at 25oC when [Fe+2] = 1.0M, [Fe+3] = 0.001M, [Cl-] = 0.003M and Pchlorine = 0.05atm

 

 

 

 

 

 

 

 

 

 

21. Calculate the values of Eo, DG and K at 25oC for the reaction in a hydrogen-oxygen fuel cell:

 

2H2(g) + O2(g) 2H2O(l)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

22. What is meant by cathodic protection? What is a sacrificial anode? Which of the following metals can offer cathodic protection to iron?

 

 

Zn Ni Al Sn

 

 

23. A constant current of 100.0 A is passed through an electrolytic cell having an impure copper anode, a pure copper cathode, and aqueous CuSO4 electrolyte. How many kilograms of copper are refined by the transfer of copper from the anode to the cathode in a 24.0 hr period?

 

 

 

 

24. Balance the following reactions

 

 

a. C2H4 + MnO4- Mn+2 + CO2 (acidic)

 

 

 

b. MnO4- + NO2- MnO2 + NO3- (basic)