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Lecture 2: Ideal Gas Law
We have briefly introduced
state variables
that unambiguously
characterize
equilibrium states of our system
, but they do NOT
describe the history of the system (how it came to these states).
Let us describe some simple systems using state variables.
Example 1
:
Consider an idealistic system with one particle (atom) in a
box. The change
of its momentum associated with scattering its from the wall is
Δ
p = 2mv
.
This event takes part once in
Δ
t = 2a/v
,
where
a
is the length of the box.
Thus the average force with which the atom acts on the walls is:
The resulting pressure is
so that
where
E
kin
is the kinetic energy of the atom.
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View Full Document Example 2
:
Consider now that a cylinder of height
h
with a liquid of density
d
is
placed in a gravitational field. The mass of the liquid is
M = Vd
= hAd,
so the force
acting on the bottom of the cylinder,
,
gives the pressure of
This results can be used to measure pressure
P
in a device called
manometer:
The difference in heights of the liquid in the two arms
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This note was uploaded on 09/23/2010 for the course CHEM 342 taught by Professor Prestonsnee during the Spring '08 term at Ill. Chicago.
 Spring '08
 PRESTONSNEE
 Physical chemistry, Equilibrium, pH

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