Physics 30 – Midterm 1 – Spring 2010
Boiling point of water (20 points)
Using thermodynamic data from the end of Schroeder’s appendix, consider 1 mole of gaseous
vs liquid water:
1.
From the relation between H and G, show that the
Δ
G
gl
,
Δ
H
gl
and S
gl
(as computed from the
table) are selfconsistent.
I am writing
Δ
G
gl
for the free energy different
Δ
G
g

Δ
G
l
; since this
is actually a difference between
Δ
G’s, chemists often write it as
ΔΔ
G.
2.
Assuming that
Δ
G,
Δ
H and S do not change with temperature, calculate the boiling point of
water at atmospheric pressure.
Your prediction will be too low because G, H and S are not,
in fact, independent of temperature.
3.
What is the energy difference
Δ
U
gl
between gas and liquid water?
Since interactions
between gas molecules are generally small (and in fact zero in the ideal gas limit), most of
this energy difference is caused by interactions in liquid water.
Liquid water is actually
enormously complex and the interaction energy (or, even worse, the entropy) is very hard to
calculate from first principles.
Nonsymmetric random walk (40 points).
Derive the advectiondiffusion equation corresponding to a
random walk with differentsized steps in the left and right
directions: leftward steps of length l occur with probability
q and rightward step of length 2l occur with probability p.
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 Spring '10
 LorenzoSorbo
 Physics, mechanics, Radioactive Decay, Energy, Random walk, liquid water

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