ADVANCED LABORATORY I
FALL, 2000
HEAT CAPACITY RATIO

Reference:   SG&N pgs. 105 - 112.

        Carry out SGN Experiment #3 (Adiabatic expansion method) with the following changes:  Measure C_p/C_v for He, N₂, CO₂.  There are three “stations”, one for each of the gases listed.  The experimenters will change stations as opposed to changing gases at each station.  This will cut down on the time needed to equilibrate/flush each system. 

            You will need to obtain certain instructions and information from your TA on the proper operation of the gas cylinders and manometers.

  Carry out the calculations described on pg. 112.  Specifically:

(1) Calculate your experimentally measured heat capacity ratio from eq. (13) in your book;

(2) For each molecule, calculate the theoretical value predicted by equipartion.  To do this, you will need to calculate C_v.  Do this in three ways as discussed in pre-lab lecture:

(a) Calculate C_v without vibrational contribution (translational and rotational only) and use this value to calculate Cp/Cv.

(b) Calculate C_v with vibrational contributions.  Do you do this for helium?  As we discussed in class, you must consider the fact that vibrational energy levels are quantized.  As a result, you cannot assume that the vibrational contribution to C_v is what one would expect from the equipartition theorem.  Instead, you must calculate the vibrational contribution to C_v using eq. 8 on pg. 386 of S,G,&N.   

You will need the following information:

(1) The energies of the vibrational modes for N₂ and CO₂:

N₂:  n₁ = 2331 cm^-1

CO₂:  n₁ = 1388 cm^-1; n₂ = 667 cm^-1(doubly degenerate, e.g. there are two modes with this energy); n₃ = 2349 cm^-1