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Storing Ammonia

  1. Nov 22, 2008 #1
    http://session.masteringphysics.com/problemAsset/1003323/16/152457.jpg

    Part A
    The line between which two points would describe a process of liquid ammonia boiling completely away?
    Express the answer as two letters representing the endpoints of the line in order so that going from the first letter to the second letter would show a process of boiling. Be careful to put the letters in the correct order.

    Okay, I got tried EG and FG already and they are both incorrect.

    Part D
    The line between which two points would describe a process of sublimation for ammonia?
    Express your answer with two letters ordered in the direction of sublimation. Be careful to put the letters in the correct order.

    I know the sublimation curve is at BC, but I don't think that's the answer they are looking for?

    Part F
    The line between which two points would describe the process of complete melting of ammonia?
    Express your answer as two letters ordered in the direction of melting. Be careful to put the letters in the correct order.

    Again, melting curve is at CD but I don't think that's what they are asking.

    Part G
    One of the most important points on a phase diagram is the triple point, where gas, liquid, and solid phases all can exist at once. What are the coordinates ( T_triple, p_triple) of the triple point of ammonia in the diagram?
    Express your answer as an ordered pair. Determine the temperature to the nearest 5K and the pressure to one significant digit.

    Part H
    At one atmosphere of pressure and temperatures above -33.3 Celsisus, ammonia exists as a gas. For transportation, ammonia is stored as a liquid under its own vapor pressure. This means that the liquid and gas phases exist simultaneously. If a container of ammonia is transported in an temperature-controlled truck that is maintained at no greater than 330K, what maximum pressure p must the sides of the container be able to withstand?
    Express the answer numerically in atmospheres to one significant figure.
     
  2. jcsd
  3. Nov 23, 2008 #2
    I don't think you're reading your phase diagram correctly. Any point that borders two phases represents a condition that allows NH4 to exist in both of those phases simultaneously. That the question specifically reads "liquid ammonia boiling completely away" means to me that they're looking for a line that would connect a point where NH4 exists entirely as a liquid to one where it is entirely a gas, without passing through the solid phase. I would also make similar assumptions about the melting and sublimation lines.
     
  4. Nov 23, 2008 #3
    But doesn't the line from E to G indicate where NH_4 "exists entirely as a liquid to one where it is entirely a gas, without passing through the solid phase"?

    And it's incorrect, I mean that is the only line possible right?
     
  5. Nov 24, 2008 #4
    Point G is entirely in the gaseous phase, but point E is straddling the interface between the liquid and gas phases, so it's not entirely a liquid. Point H, however...

    BTW - before somebody gives me grief for a bad chemical formula, NH4+ is technically the ammonium ion, where NH3 is the correct formula for ammonia. That's what I get for posting past midnight. :)
     
    Last edited: Nov 24, 2008
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