CH353 - Physical Chemistry I
Spring 2012, Unique 52135


Homework, Week 3


Homework, week 3
Answer key

1.  A chemical reaction takes place in a container with a cross-sectional area of 1 m2.  As a result of this reaction, a piston is pushed out 500 cm against an external pressure of 1.0 atm.  Calculate the work done by the system.

2.  A 1 L sample of 2.00 mol Ar gas is expanded isothermally at 0˚C to a final volume of 5 L a) reversibly, b) against a constant external pressure equal to the final pressure of the gas, and c) freely (against no external pressure).  Determine q, w, deltaU, and deltaH for these three processes. 

3.  (To see the following equations most clearly, you should download a copy of the pdf.) A monatomic gas obeys the following equation of state:

    P(Vm-b) = RT

Show that for a reversible, adiabatic expansion of a monatomic gas,

    (Tf/Ti)^(3/2) = ((Vmi-b)/(Vmf-b))

(Hint, knowing the expansion is adiabatic, find simple expressions for dw and dU and equate them.)

4.  1.00 mol of a monatomic ideal gas is initially held at 300 K and 1.0 atm.  The gas is heated to 400 K reversibly at constant volume.  Determine q, w, and deltaU. 

5.  An ideal monatomic gas at 273.15 K and 1 bar is expanded adiabatically from 22.7 L to 45.4 L.  What is the final temperature of the system?

6.  If you were on the surface of the moon you would need to wear a space suit with thermal insulation.  In exploring the moon you might generate 4 kJ of heat per kg of mass per hour.  If your body retains all of this heat because the insulation, how much would your temperature change per hour during this activity?  How long would you recommend for such a moon walk?  Assume your body mass is 65 kg and that your heat capacity is approximately that of water (Cp,m(H2O(l)) = 75.29 J K-1 mol-1).