Chem 203

First Exam-Part B

Monday October 9, 1989

 

Name____Gibbs____

R = 8.314 J/K mol

= 1.98 cal/K mol

= 0.082 lt atm/K mol

Full credit will be given to correct answers only when ALL the necessary steps are shown.

This is an open book, open notes exam, and you are responsible to be sure that your exam has no missing pages(7 pages).

The exam is due Wednesday October 11, 1989.

If you consider that there is not enough information to solve a problem, you have to specify the missing information and describe the problem solving procedure.

 

 

Honor Statement

I have neither give nor received aid in this examination.

Full signature _______________________________

Problem 1.- a)- How many calories of food energy are required for breathing each day, assuming that one inhales an average of 0.5L of air 15 times/min against 1-atm pressure? (Hint: 1L-atm = 24.2 calories)

b)- If 30% of the O2 inhaled is consumed, what percentage of the energy generated from the O2 consumed is used to operate the lungs? (Assume O2 is used to oxidize sucrose to CO2 and H2O.)

 

Problem 2.- Calculate the P-V work done in calories when a sphere of water 1 mm ( 1mm = 10-4 cm ) in diameter freeze to ice at 0 oC and 1 atm. pressure.

 

Problem 3. The Van der Waals constants for O2(g) are

a = 1.360 L2 atm mol-2

b = 3.183 x 10-2 L mol-1 .

Suppose 2.000 mol of O2(g) expands reversibly and isothermal at 300.0 K from an initial volume of 1.00 L to a final volume of 10.0 L. Calculate the work done by the gas and compare with the work done by an ideal gas that expands reversibly and isothermally between the same initial and final states. What is the molecular level explanation of the difference in the work values for the two cases?

 

Problem 4. - Given the following equation of state for a gas,

 

 

where a and b are constant, and the virial expansion of argon at 273 K,

 

calculate the critical constants of argon.

 

Problem 5. - Two equal blocks of the same metal, one at Th and the other at Tc , are placed in contact and come to thermal equilibrium. Assuming the heat capacity to be constant over the temperature range at 24.4 J K-1 mol-1 , calculate the change of entropy. Calculate the value for the case of two 500 g blocks of copper, with Th = 500 K and Tc = 250 K.

 

Problem 6.- Calculate the standard enthalpy, DHo, and the standards Gibbs energy, DGo, for the combustion of hydrazine, NH(l) + O(g) -- > N(g) + 2HO(l), both at 298 K. Estimate the standard Gibbs energy at a) 1000K and b) 100 K.

i) Is the reaction spontaneous at room temperature

ii) Is the reaction favored by a rise in temperature?

Assume that DHo is independent of the temperature.