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!

Am I doing this vapour pressure problem correctly?

  1. Aug 30, 2015 #1
    1. The problem statement, all variables and given/known data
    'The vapour pressure of ethanol (C2H5OH) at 19°C is 40.0 torr. A 1.00-g sample of ethanol is placed in a 2.00 L container at 19°C. If the container is closed and the ethanol is allowed to reach equilibrium with its vapour, how many grams of liquid ethanol remain?'

    2. Relevant equations
    PV = nRT
    R = 62.36 L⋅torr / mol⋅K

    3. The attempt at a solution
    Basically, when I tried to plug in all the numbers into the ideal gas equation (with the given mol number of 1/46), it wasn't quite equal. Then I figured, that not all the ethanol is converted into vapour; only some of it. And this equation really only applies to gases (a.k.a. vapours). I didn't know how much, so that's basically what I set out to find out with what I was given.

    (40.0 torr)(2.00 L) = (x mol)(62.36 L⋅torr/1 mol⋅K)(292 K)
    80 L⋅torr = x19209.12 L⋅torr
    x = 0.0044 mol C2H5OH (g)
    0.0044 mol(46.06844 g/1 mol) = 0.203 g C2H5OH (g)
    1.00 - 0.203 = 0.797 g C2H5OH (l)
    Last edited: Aug 30, 2015
  2. jcsd
  3. Aug 30, 2015 #2


    User Avatar

    Staff: Mentor

    Looks OK to me.
  4. Aug 30, 2015 #3
    Thank you.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted