Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Thermodynamics: Calculating Pressure Increase From Work

  1. Nov 3, 2017 #1
    1. The problem statement, all variables and given/known data
    Estimate the pressure increase required to impart 1 J of mechanical work in reversibly compressing 1 mol of silver at room temperature. What pressure rise would be required to impart 1 J of work to 1 mol of alumina at room temperature? For alumina take the molar volume to be 25.715 (cc/mol) and (BETA)=8*10^(-7) (atm)^(-1).
    For silver, the molar volume is 10.27 (cc/mol) and (BETA)= 9.93*10^(-6)
    Beta is the coefficient of compressibility

    2. Relevant equations
    Mechanical Work= -PdV

    3. The attempt at a solution
    I assumed that temperature remained constant during this process. I know that the answer should be 9.6*(10)^6 atm for silver and 978 atm for alumina. I have been getting 140041 atm for silver and 311800 atm for alumina. The attempt is attached below. Any ideas as to what I'm doing wrong? Thanks in advance!
  2. jcsd
  3. Nov 3, 2017 #2
    I can't open your attachment. Have you uploaded the file?
  4. Nov 3, 2017 #3
    Sorry, thought I attached the image to the original post

  5. Nov 3, 2017 #4
    I just realized what I was doing wrong. I needed to convert the mechanical work (in Joules) to units of cm^3 atm. This gives me the right answer for alumina, but I'm getting 1461.34 atm for silver. Attached below is the work with the conversions in mind

  6. Nov 3, 2017 #5
    This result doesn't seem to agree with your result shown on the paper. Please show your work, including the substitutions.

    I confirm the 979 atm for alumina. For silver, from the data given, I get 440 atm.
  7. Nov 3, 2017 #6
    Here's the work for the silver sample, I'm still getting 1461 atm
  8. Nov 3, 2017 #7
    It looks like you used the wrong value of beta in your calculation. Otherwise, nicely done.
  9. Nov 3, 2017 #8
    Okay, thank you!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted