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Homework Help: Physical and analytical chemistry

  1. Aug 10, 2009 #1
    1. The problem statement, all variables and given/known data
    A rigid container,maintained at 50 degree celcius, is evacuated by a vacuum pump. After this, some liquid n-propanol is introduced into the container. part of the liquid will flash off inside the vacuum,but eventually the system will settle into equilibrium.
    what is the expected pressure of the system in mmHg?why?

    3. The attempt at a solution
    the ecpected pressure may be 760mmHg
  2. jcsd
  3. Aug 10, 2009 #2
    I remember problems similar to this I think they where solved with the Clausius Clapeyron relation ship, formulated to relate pressure to temperature using the delta H of vapourisation. Most versions of this relationship relate a pressure ratio to a temperature change. A quick search and I found it in wikipedia. It looks correct but its a long time since I have done anything like this. Does this sound familiar to you?

  4. Aug 10, 2009 #3
    hmmm..not really.
  5. Aug 12, 2009 #4
    Well when the propanol is introduced into the container Some of it vaporises. It reaches equilibrium when the rate of vaporisation = .............. you finish this.

    The page I posted contains a formula which relates equilibrium pressure to temperature. Look through the whole page and you will find it.
  6. Aug 12, 2009 #5


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    Staff: Mentor

    Clausius-Clapeyron relation - although can be used - is not enough just by itself, you need additional data (like vaporisation enthalpy) for that - and these can be found in tables.

    As you have to consult tables, why not look directly for the table of vapor pressures of n-propanol for different temperatures?

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