As per request:
Liquid Hydrogen Water Methane Ammonia
Property H2 H2O CH4 NH3
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Boiling point
C -252.87 0.00 -164.0 -33.35
K 20.28 273.15 109.15 239.80
Density at b.p.
(kg/m^3) 70.0 1000.0 424. 682.1
# of molecules
(moles/m^3) 34724 55508 26429 40052
# of H atoms
(moles/m^3) 69448 111016 105716 120156
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ratio
(LH2 = 1) 1 1.599 1.522 1.730
These are the correct numbers at the respective boiling points.
The densities are bound to change with temperature, but I don't
have those sorts of charts handy. Oh yeah, all at 1 atm.
Apparently I was in error about the density of Methane. Too
bad. Ammonia takes the top spot again. Hmm, what about solid
methane and ammonia ice...
The numbers are from the CRC Handbook of Chemistry and Physics,
67th edition, 1986-1987, page B-447. Great book. Everyone
should read it at least once through :-).
As James pointed out, all materials don't have the same number
of molecules per unit volume. Sometimes the trend is counter-
intuitive (tiny H2 molecules occupy a lot of space). I never
did well on that chapter on attractive/repulsive forces so that's
the best answer I can give. Remember all that stuff you learned
about ideal gases? Trash it. It only works well for noble gases.
All the other gases act really strange.
- --
John H. Kim
[email removed]
[email removed]