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!

Physical Chemistry- Partial Pressures

  1. Oct 13, 2012 #1
    Hello all,
    This is a homework problem for my CHE345 class. Not sure what to do here, please at least let me know if I'm in the right ballpark.

    1. The problem statement, all variables and given/known data

    A student decomposes KCLO3 and collects 35.2 cm^3 of O2 over water at 23.0°C. The laboratory barometer reads 751 Torr. The vapor pressure of water at 23.0°C is 21.1 Torr. Find the volume the oxygen would occupy at 0.0*C and 1.2atm (= 912 Torr).

    2. Relevant equations
    not exactly sure what is relevant here. Perhaps these:
    (1) PV = nRT
    (2) Pj = partial pressure
    (3) xj = mole fraction
    (4) Pj = xjP
    (5) Pj = njRT/V
    (6) Ptotal = PA + PB +.....

    3. The attempt at a solution
    My problem I think, is in interpreting the question, but here goes an attempt:

    using eq. (6):
    Ptotal = Pwater + PO2
    751 Torr = 21.1 Torr + PO2
    PO2 = 729.9

    from here I'll use eq. (1) to solve for nO2
    PV = nRT
    n = PV/RT
    n = (729.9 Torr)(0.0352 L)/(62.634 L Torr K-1mol-1)(296.15 K)
    n = 1.385 x 10-4

    Now to solve for the V at Tfinal

    V = nRT/P
    V = (1.385E-4 moles)(62.634 L Torr K-1mol-1)(273.15 K) / 912 Torr)
    V = 0.002598 L = 2.598cm3

    How'd I do?
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Oct 13, 2012 #2
    You made an arithmetic error in calculating the number of moles. The pressures and temperatures in the two situations are not too different, and, if the volume was much less than 35.2 cc, this should have alerted you that there was an arithmetic mistake somewhere. Try to get used to asking yourself whether your answer makes sense.
     
  4. Oct 13, 2012 #3
    1. The problem statement, all variables and given/known data

    A student decomposes KCLO3 and collects 35.2 cm^3 of O2 over water at 23.0°C. The laboratory barometer reads 751 Torr. The vapor pressure of water at 23.0°C is 21.1 Torr. Find the volume the oxygen would occupy at 0.0*C and 1.2atm (= 912 Torr).

    2. Relevant equations
    not exactly sure what is relevant here. Perhaps these:
    (1) PV = nRT
    (2) Pj = partial pressure
    (3) xj = mole fraction
    (4) Pj = xjP
    (5) Pj = njRT/V
    (6) Ptotal = PA + PB +.....

    3. The attempt at a solution
    My problem I think, is in interpreting the question, but here goes an attempt:

    using eq. (6):
    Ptotal = Pwater + PO2
    751 Torr = 21.1 Torr + PO2
    PO2 = 729.9

    from here I'll use eq. (1) to solve for nO2
    PV = nRT
    n = PV/RT
    n = (729.9 Torr)(0.0352 L)/(62.634 L Torr K-1mol-1)(296.15 K)
    n = 1.385 x 10-3

    Now to solve for the V at Tfinal

    V = nRT/P
    V = (1.385E-3 moles)(62.634 L Torr K-1mol-1)(273.15 K) / 912 Torr)
    V = 0.02598 L = 25.98cm3

    Ah yes, thank you, I missed a digit. That better? Did I go about the problem correctly?
     
  5. Oct 13, 2012 #4
    Yes. Nice job.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Physical Chemistry- Partial Pressures
  1. Partial Pressures (Replies: 16)

Loading...