PHY-0002 Lecture Notes - Triatomic Molecule, Waste Heat, Thermodynamics
28 Mar 2014
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In class we derived the molar specific heats for an ideal monatomic gas at constant pressure and at constant volume (see p. 621-623) and showed that: We can also look at the molar specific heats of diatomic and tri-atomic gases, using experimental data listed in table 20-1 of giancoli"s book general. The next slide shows selected entries from that table. Note that the units are in (cal/mol. -k) instead of the usual (j/mol. -k). The ratio of the heat capacities is important because it determines the slope of adiabatic curves on the p-v diagram for the gas. This ratio is usually labeled (greek letter gamma ). 5/3 = 1. 67 , since cv=(3/2)r and cp=(5/2)r. For diatomic gases, = (7/5) = 1. 40, since cv=(5/2)r and cp=(7/2)r due to the two additional rotational degrees of freedom. For co2 the value of is 1. 30, since it is a tri-atomic molecule. The p-v curve for an adiabat is given by where.
