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Homework Help: Question on Thermal Physics.

  1. Jun 24, 2011 #1
    Not homework, just need some help with explaining the effect of the following 2 things on the melting point/freezing point and boiling point of water;

    1. Pressure is increased
    2. Impurities are added

    If possible, can the explanations be as explicit as possible?? I have really no idea how to work on it and any help is greatly appreciated. Thanks!:smile:
  2. jcsd
  3. Jun 24, 2011 #2
    What do you think happens?

    Obviously boiling, freezing, melting points are linked to a specific temperature. What relationships does pressure have to temperature?

    How do you think impurities would affect the properties of a material?
  4. Jun 24, 2011 #3
    From my notes, Pressure is proportional to Temperature (Pressure's Law). I know that the boiling point of water will increase if the pressure increases, because more energy is needed to overcome the intermolecular forces of attraction between water molecules as well as to overcome the increased pressure.
    For pressure affecting the melting/freezing point, my notes just say that increased pressure will cause the melting/freezing point to become lower, but they don't explain why.
    For impurities, the notes only mention about the boiling point increasing and the melting/freezing point decreasing, also not explaining why.
    Is there any way i can apply Pressure's Law (Pressure proportional to Temp.), Charle's Law (Volume proportional to Temp.) and Boyle's Law (Pressure inversely proportional to Volume)?

    My take on pressure affecting the melting/freezing point of water is that when pressure is applied to ice, the temperature of the ice will increase (Pressure's Law). When temp. increases, it melts and the volume also decreases (Boyle's Law). So does that mean that for water to become ice again, it will have to lose more energy, thus a lower melting/freezing point? That's where I am left clueless. My understanding of the concept isn't really there yet.

    As for impurities, I have really no idea how to start as my notes are just too brief and do not explain anything.
  5. Jun 24, 2011 #4


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    Staff: Mentor

    In situations where your notes are too brief, or confusing, there are plenty of online resources you can consult. A good one is http://ask.com where you type in your question, and it comes up with lots of links. Ignore those which are clearly off topic, and refer to some which address your question. Read at least 4 or 5 of the sources, because, after all, this is the web and not all authors are as well-intentioned or as well-informed as we'd hope.

    A suitable question to put to ask.com is: how do impurities affect the freezing point of water?
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