At ordinary temperatures many of the excited state rotational levels are thermally accessible and hence the rotational contribution is in accord with the equipartition theorem of classical mechanics. Thus, it is possible to calculate definite values for C V and hence, through the ideal gas equation of state, the ratio for ideal monatomic and polyatomic gases using the above expressions. A two step process can be used to experimentally determine the ratio of the heat capacities. The thermodynamic expressions used to derive the heat capacity ratio apply only to the part of the gas that remains in the carboy after the stopper is replaced since molar volumes and molar heat capacities were used. The gas below this surface expands in an approximately reversible way against the surface.
Work is done as the upper gas is pushed out.
The change is approximately adiabatic only because it is rapid copared to heat flow but slow on the scale of the mechanical work. No appreciable amount of heat is transferred between the reservoir and the gas in the carboy during the short period of the expansion, but after the stopper is replaced, the temperature is seen to increase as thermal equilibrium is reestablished for the gas remaining in the vessel. The lab is equipped with several apparati as shown above, each filled with a different sample gas. Student teams shall rotate through the stations so that each team may obtain data on all the sample gases. This data will be used to correct for drift of the 'zero' of the electronic pressure gauge.