220.
Problem 24.5 (RHK)
At standard temperature and pressure ( and 1.0 atm) the mean free path in helium gas is 285 nm. We have to determine (a) the number of molecules per cubic meter and (b) the effective diameter of the helium atoms.
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(a)
The equation of state of an ideal gas in terms of the total number of molecules N at temperature T, pressure P and volume V is
or
(b)
The mean free path is determined by the number density of molecules and the effective molecular diameter d by the relation
We are given that the mean free path in the helium gas at the standard temperature and pressure is
Therefore,
and 1.0 atm) the
mean free path in helium gas is 285 nm. We
have to determine (a) the
number of molecules per cubic meter and (b)
the effective diameter of the helium atoms.
is determined by the number density of molecules
and the effective molecular diameter d by
the relation
