1. Not finding help here? Sign up for a free 30min 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!

Taking the derivative of the van der waals equation

  1. Oct 27, 2011 #1
    1. The problem statement, all variables and given/known data

    I'm trying to find dT/dVm for the van der waals equation. I was looking at http://courses.washington.edu/bhrchem/c456/vdw_jtc.pdf" [Broken] page, but I'm confused about how they reached their result:

    Bkw5k.jpg


    3. The attempt at a solution

    I honestly have no idea what they did. dT/dVm of RT(Vm-b) is obviously -RT/(Vm-b)^2, and dT/dVm of -a/Vm^2 is 2a/Vm^3, and dT/dVm of P is 0, but I have no idea where [R/(Vm-b)](dT/dVm) came from. Am I missing something obvious here? It's been a while since calc.
     
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Oct 28, 2011 #2

    Fredrik

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    The first term is the product of RT and 1/(V_m-b), so you need to use the product rule: (fg)'(x)=f'(x)g(x)+f(x)g'(x).
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Taking the derivative of the van der waals equation
Loading...