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Some question need to be solved

  1. May 21, 2005 #1
    some question need to be solved!!!!!

    1.) A container contains 60cm3 of CO2 and 40cm3 of O2 at room temperature and pressure conditions. If 200cm3 of H2 at room temperature and pressure is now injected into the container, which of the following would happen? :confused:
    (a) The partial pressure of O2 will decrease
    (b) The total pressure of the gases in the container will increase
    (c) The partial pressure of CO2 and O2 remain constant
    The answer given is (b) & (c),why?how to count?Please show the calculations. :smile:

    2.) When a few crystals of ice are added to supercooled water at -5 degree Celcius,which of the following would happen? :confused:
    (a) More ice is precipitated
    (b) The vapour pressure increases
    (c) The temperature of the water increases
    The answer given is (a),(b)&(c),why?Please provide me some explanation. :smile:
  2. jcsd
  3. May 21, 2005 #2


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    1)From now on you'll need to show some work, the answer is fairly simple, pressure is a directly consequence of temperature and moles of the ideal molecule in question, neither will change with the addition of a separate gas at the same temperature.

    2)Ice freezes at 0 degrees, what happens if supercooled liquid is disturbed? The answer should be obvious, it can be found in your text. The rest...epiphany
  4. May 21, 2005 #3

    sorry,i still don't get what u mean.
    the first question,i had already count,but i just can't get the answer,that's why i need someone to show the calculations for me.thanks
    for the second one,i need some explanation,i don't want to just accept the answer,but i want to know why.if i just accept the answer given,what have i learn?nothing at all. :confused:
  5. May 21, 2005 #4
    number 1 is pretty easy, think about it, gasses dont aquire different pressures, so if you inject more gas (no matter what it is) into a container whcih does not change shape the pressure of the whole thing goes up...

    i think,
  6. May 22, 2005 #5


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    well no calculations are needed. question number 1 indicates that the gaseous hydrogen is at the same temperature as oxygen and carbon dioxide, there will not be change in temperature, just a change in the net pressure. Furthermore, adding the gas does nothing to change the number of molecules and the temperature of oxygen and carbon dioxide, remember P=nRT/V...V, R, n, and T are all constant for oxygen and carbon dioxide despite the addition, thus their contribution to the partial pressure remains the same.

    Again, for the second one....read your text. Search through the index for supercooled liquids, it should give you an explicit answer. Especially pay attention to when they explain what happens when a supercooled liquid is disturbed. If you still can't figure it out, then I'll be glad to help you out.
  7. May 22, 2005 #6
    thank you

    thank you for your explanation.I hope u don't mind if u can tell me the total pressure that CO2 and O2 exerted before H2 is added in. :wink:

    i found out that the website that u recommend me is very useful,especially the MSN one,that is for general chemistry ,right?
    can i know the same MSN one for biology and math??? :smile:

    anyway,thanks alot for helping me,u r so kind. o:)
  8. May 22, 2005 #7


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    yep it's for chemistry, but you can also ask organic I, II as well as the labs. I don't know of any biology or math MSN forums that are quite active. The biology forums here at PF are certainly nice and definitely the math subforum, it it is not sufficient you can try http://www.mathforums.com, especially a lot of active math forums out there.

    Did the original question imply standard temperature and pressure? Standard pressure is 1 atm, that's a given, the wording of the question is not so clear, but I'm guessing

    [tex]P_{o2}+P_{co2}=1 atm[/tex]

    Again, the question does not emphasize calculation.
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