Pr and Vr: Ideal Gas Property Tables

Ch 7, Lesson E, Page 3 - Pr and Vr: Ideal Gas Property Tables

• Take a closer look at these two equations.  Remember that So is function of temperature, ONLY.
• Consequently, Vr and Pr are also functions of temperature ONLY.
• So, we might as well tabulate them in the ideal gas entropy tables and that is exactly what we did.
• You can find a copy of the Ideal Gas Entropy Tables in the Chapter 7 First-Aid Kit.
• A small chunk of the table is shown here.
• U-nought and Ho are just the integral of CV and CP, respectively, from the reference temperature to the temperature listed in the 1st column of this table.
• These are easy to use.  For example, DH-wiggle for air in an ideal gas state when it goes from 300 Kelvin to 350 Kelvin is just 1507.37 – 53.44 which is equal to 1453.93 J/mole.
• This table was created from the heat capacity polynomials on the NIST website, so, as long as you don’t have to interpolate to find the temperature you need, the ΔHwiggles and ΔUwiggles that you calculate are every bit as accurate as if you used the polynomials yourself.  But these tables are much quicker, especially if you aren’t using a computer.
• But, if you have to interpolate to find the temperature that you need, then your answer will be less accurate than if you used the polynomial heat capacities.
• OK.  Now, how do we use Vr and Pr.  That’s what we are really interested in at this point.
• Flip the page and you’ll see.