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Homework Help: Gas laws Haber process

  1. Jun 9, 2013 #1
    Hello everyone,
    I'm doing some practice problems for my final exam.
    I came across this question:

    «The Haber process is being used at a pressure of 76 000 mmHg at a temperature of 450°C. Gaseous ammonia is cooled and collected after its production, in order that its temperature does not exceed 132,35°C.
    What is the maximum pressure in kPa that ammonia must be in to not exceed that temperature? »

    So, the answer key of the previous exam I took it from says 5680 kPa. However, I find that a bit weird. It's a basic application of P1/T1=P2/T2... First of all, isn't 76 000mmHg the pressure of all the gases, including H2 and N2? Then, it is said that ammonia is collected, changing the volume of the recipient? What do you think?
  2. jcsd
  3. Jul 13, 2013 #2
    Since no one has answered so far: I don't know the answer for sure, but I cannot think of anything else to do with the given data... You have some ammonia at 450 C. You want to cool it to reach 132,35 C. What will be the final pressure? You need to know the initial one which cannot be other that 76000 mmHg because you do not have any data to calculate an use another value...
    Last edited: Jul 13, 2013
  4. Jul 14, 2013 #3
    This is a continuous process and I'm assuming that some or all of the ammonia produced at any instant enters a part of the reaction vessel where the pressure is reduced sufficiently. This can result in the cooling necessary to liquify and remove that ammonia.
    Application of the ideal equation P1/T1=P2/T2 does give a pressure of 5680kPa as in your answer key so I assume that is all that is needed to answer the question.
    It does seem very odd though. The deviations from ideal gas behaviour are enormous within the environmental conditions met in the reaction vessel.
    Last edited: Jul 14, 2013
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