Physics Help Forum [SOLVED] Density, Mass and Volume

 Thermodynamics and Fluid Mechanics Thermodynamics and Fluid Mechanics Physics Help Forum

 May 26th 2010, 06:55 AM #1 Junior Member   Join Date: Oct 2009 Posts: 24 [SOLVED] Density, Mass and Volume Q) The density of liquid water is 1.0 g cm^-3. The density of water vapour at atmospheric pressure is approximately 1/1600 g cm^-3. Determine the ratio (i) volume of water vapour / volume of equal mass of liquid water (ii) mean separation of molecules in water vapour / mean separation of molecules in liquid water My Attempt I've got the correct answer of (i) which is 1600:1 but can't figure out what (ii) means or how to solve it. Thanks in advance!
 May 29th 2010, 11:43 PM #2 Physics Team   Join Date: Feb 2009 Posts: 1,425 Take 1 mole of H2O. This contains Avogadro's no of molecules. Since you know the densities of water vapour and water, find the corresponding volumes, and then divide them by the Avogadro number to get the mean seperation.
 May 30th 2010, 12:57 AM #3 Junior Member   Join Date: Oct 2009 Posts: 24 Thanks, but this is a Physics question and it shouldn't require chemistry equations to solve it. I've got it though, we just take the cube root of the volumes in such questions.
Jun 2nd 2010, 12:03 AM   #4
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 Originally Posted by unstopabl3 Thanks, but this is a Physics question and it shouldn't require chemistry equations to solve it. I've got it though, we just take the cube root of the volumes in such questions.
This is a typical case one might find in the thermodynamics section of a physics textbook.

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