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Homework Help: Simple Chemistry Q's

  1. Apr 7, 2005 #1
    Hey guys, I have a few questions that i'm having a little trouble with, I'm hoping someone can help. The only course that I'm really weak in is chemistry, so please..no one laugh :approve:

    Ok so here it goes

    1) A cylinder contains a mixture of hydrogen and chlorine molecules. Compare without doing any calculations:

    a) the relative mass of the molecules
    b) the temperature of each gas
    c) the average kinetic energy of the molecules
    d) the average speed of the molecules

    I just dont understand what I have to do in this one or where I get the answers.

    Here's the second question...

    2) Find the number of atoms in

    a) 25.5g of calcium metal
    b) 1.5 mol of carbon
    c) 1.5 of carbon dixide

    I'm also not sure of this one, Is there a formula that i'm supposed to use?

    3) Find the volume of a gas at -30C and 0.75 atm if it occupies a volume of 255 L at 40.0C and 1.25 atm.

    I'm pretty sure I have to use Charle's Law, but again, not completely sure.

    I'd also like to add that I'm learning Chemistry by myself, with no help from anyone except you guys, so thanks in advance to everyone
  2. jcsd
  3. Apr 7, 2005 #2
    Well right off the top of my head for number one:

    The realitve masses of each element is simple, just look at a peroidic table, H is about 1AMU and CL is aroundl 35 AMU.

    For B-D they all depend on if your "system" is at STP. If it is then the Temperature would be 273K, Pressure = 1ATM. From that you could estimate that KE of each element is going to be greater for the less masisve element. The total KE for the system however is the same being that all the collisions are elastic. The average speed is dependent upon the mass ssoo the Speed is higher for the H atom than the Cl. Look up the RMS equation for asimple explination( Root Mean Spuare).

    Hope this helps

    Also just looking at 3) i'd say you need the combined gas law, look it up in your chem book.

    ------ 2) -----

    I just looked now and iwhat you do is conver whatever your looking for into moles and multiply it by Avogadro's number.
    Last edited: Apr 7, 2005
  4. Apr 7, 2005 #3


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    I can't say I understand this statement. Who's giving you all this homework, and why aren't they teaching you anything ?

    You really need to learn your basics to answer the questions you have - they are mostlly very fundamental, and giving you the answers would not help in any way.

    Surely, your textbook will cover the necessary material. If you don't have a text, look into http://members.tripod.com/~EppE/ (Ch. 5 & 6 are important)
  5. Apr 7, 2005 #4
    decibel check your messages..i left you one!
  6. Apr 7, 2005 #5


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    For the last,u need Mendeleev-Clapeyron's equation...Charles's law is useless.

  7. Apr 8, 2005 #6


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    1.a) Like spectre said, look at the periodic table;
    b) Unlike spectre said, it's a mixture, it's presumed to be at thermal and mechanical equilibrium (it ain't chemically), and the hydrogen molecules are at the same temperature as the chlorine molecules;
    c) Kinetic energy of molecules in the gas phase is a function of temperature, fixed temperature fixing the kinetic energy of any gas molecule ("any" means anything from hydrogen to however heavy you can get and still get into the gas, vapor, phase;
    d) Like spectre said, rms.

    2. Reread what your text says about Avogadro's Number, and, for 3. the ideal gas equation of state (or ideal gas "law").
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