1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Ideal gases thermodynamic enthalpy and internal energy change

  1. Jan 21, 2012 #1
    1. The problem statement, all variables and given/known data
    See attachment ecxample001.

    2. Relevant equations

    See attachment D11.

    3. The attempt at a solution
    In the first equation (Cp/R = a+bT+cT^2...etc.), Cp/R is the constant pressure specific heat. The general formula for enthalpy change is h2-h1 = integral[Cp]dT, so does Cp/R = Cp except Cp/R is the constant pressure specific heat on a molar basis?

    Then in the next line of formula in the solution (h2-h1 = R/M integral (a+bT...)dT) how did it go from Cp/R to R/M? I'm totally lost in this. And by the formula do I seriously plug in these huge numbers (from D11)? I tried plugging it in and get keep getting somethign to the 17th power. I'm also very confused on the units, as there's a lot of variables and I'm not very clear on them and what they represent. Any help would be appreciated. Thanks!
     

    Attached Files:

  2. jcsd
  3. Jan 21, 2012 #2
    It looks like the numbers in the chart are intended to be between 1 and 25 in absolute value. Values for b are premultiplied by 1000. C by 1M and d by 1B. So the value d for CO2 would be 2.002X10^-9.
     
  4. Jan 21, 2012 #3
    thanks i know that from the chart. So how did the problem go from cp/R to R/M?
     
  5. Jan 21, 2012 #4
    Enthalpy change is integral of CpdT. They give you Cp/R as function of temperature on a molar basis. So Cp is R times the polynomial. The M comes from the fact it is a mass basis.
     
  6. Jan 21, 2012 #5
    So R/M is merely a conversion factor to get Cp molar basis back to the regular Cp?
    Thanks a lot man.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Ideal gases thermodynamic enthalpy and internal energy change
  1. Change in enthalpy (Replies: 4)

Loading...