CHEM 4010                                                                                              Name___________

Dr. Perona                                                                                                 April 13, 2005

Hour.Exam 2

 

 

R = 0.08206 L atm-1 K-1 mol-1 = 8.413 J K-1 mol-1

1 atm = 1.01325x105 N m-2

1 m3 = 106 cm3 = 103 L

1 L atm = 101.32 J

Thermodynamic data at 298 K

Compound

DfGo/ kJ mol-1  

Smo/ JK-1 mol-1

C2H5OH(l), ethanol

-174.78

160.7

H2(g)

 

130.684

O2(g)

 

205.138

C(s), graphite

 

5.740

H2O(l)

-237.13

69.91

CH3OH(l), methanol

-166.27

126.8

CO2(g)

-394.36

213.74

 

Do all of the problems, 1 through 8.  You must show all of your work clearly to obtain full credit.

 

1.       (10) Define the term absolute entropy, and explain why the absolute entropy can never have a negative value.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  1. (13) Given the equation ,

 

a)      show clearly and in detail that , and

 

 

 

 

 

 

 

 

 

 

 

b)      go on to derive, again clearly and in detail, the Maxwell relation:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

3.       (13) Determine the standard molar entropy of formation, DfSo, for liquid methanol, CH3OH(l),  at 298.15 K.  You will need the thermodynamic data on the first page of this exam.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

4.       (12) Ethanol has been proposed as a possible fuel for automobiles.  What is the maximum amount of non-pV work that can be obtained from the combustion of 1.00 mol of liquid ethanol at 298.15 K?  You will need the thermodynamic data on the first page of this exam. The reaction is:

 

C2H5OH(l) + 3 O2(g) ® 2 CO2(g) + 3 H2O(l)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  1. (13) One mole of solid water (ice), initially at –10.0 oC and 1 atm, is converted to the liquid at 25.0 oC and 1 atm.  What is the entropy change of the water in this process?  The heat capacities of ice and liquid water are 37.7 and 75.3  J K-1 mol-1, respectively. The enthalpy of fusion of water at its melting point of 0.00 oC is 6.01 kJ mol-1.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

6.       (13) In one cycle, a Carnot engine takes in 600 J of heat from a high temperature reservoir at

120 oC, performs 200 J of work, and discharges the remaining heat to a low temperature reservoir.

 

            a)   What is the efficiency of the engine?

 

 

 

 

 

 

b)   What is the temperature of the low temperature reservoir?

 

 

 

 

 

 

c)      What must the temperature of the low temperature reservoir be to achieve a complete conversion of heat into work?

 

7.       (13) The standard molar entropy of O2, So, at 298.15 K is 205.0 J K-1 mol-1.  This is the entropy of one mole at 298.15 K and 1 bar. Assuming that O2 is an ideal gas, what is the molar entropy of O2 at 298.15 K and a pressure of 100 bar?

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

8.   (13) Calculate the change in entropy when 25 g of water at 90 oC is poured into 25 g of water at 20 oC in an insulated vessel, given that for water, = 75.3 J K-1 mol-1, and the molar mass is 18.02 g/mol.