NORTH CAROLINA STATE UNIVERSITY

Department of Chemistry                                                Name________________________________

 

CH 431                                                                                                                Practice Mid-term 2

Physical Chemistry I                                                                                                                            

 

Given:                           g = 9.81 m/s2

                                    R = 8.314 J mol-1 K-1 = 0.08206 L atm mol-1 K-1

                                    1 atm = 1.0133 x 105 Nm-2 = 760 Torr

                                    P = P0exp{-Mgh/RT}


 


                                     

Please answer all questions.

 

1.      a. Calculate the entropy change for the system, surroundings and the total entropy change for the isothermal expansion of an ideal gas from 1.5 L to 4.5 L against a constant external pressure  of 3 atm.

b.      Calculate the thermodynamic efficiency of steam turbine operating at 370 K if the temperature at the outlet is 300 K.

c.       The molecule CHClBrI can exist in two enantiomers.  Assuming that this molecule and its enantiomer can both adopt any one of four configurations in the low temperature crystalline form (which is a racemic mixture), calculate the residual entropy of one mole of CHClBrI in this imperfect crystalline form at 0 K.

 

 

2.     Oxygen, nitrogen, and argon gases are placed in an insulated vessel with volume V with a gas tight seal dividing the vessel into three equal volumes. The seal is removed reversibly and the three gases are allowed to come to equilibrium.

 

 

a. Calculate the entropy of mixing.

b. Calculate the entropy change associated with the volume change as argon is expanded from the initial to the final volume.

c. Calculate the entropy change associated with the volume change as oxygen is expanded from the initial to the final volume.

d. Calculate the entropy change associated with the volume change as nitrogen is expanded from the initial to the final volume.

 

e. Compare the entropy change of the expansion of the individual gases with the entropy of mixing.  What can you conclude?

 

3.      Find an expression for (H/P)T for (a) an ideal gas (b) a van der Waals gas.

 

4.      The standard enthalpy of the reaction O2 (g) + 2 H2 (g) ® 2 H2O (l) is – 571.6 kJ/mol of water and the third law entropies of H2, O2, and H2O at 298 K are given in the table below.  Assuming that the entropy and enthalpy are independent of temperature calculate the Gibb’s free energy at 1000 K.  The enthalpy of vaporization of water is DvapH = 40.7 kJ/mol.  Given the heat capacity data below calculate the Gibb’s free energy at 1000 K based on the temperature dependence of the enthalpy and entropy.

 

Substance

Cp (J/mol-K)

S (J/mol-K)

H2O (l)

75.3

70.0

H2O (g)

30.54

-----

H2 (g)

27.28

130.6

O2 (g)

29.96

205.1