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Terminology:
Spontaneity
:
The notion of whether or not a
process can take place unassisted. (E.g. Rock
rolling down hill; iron rusting; heat flow from hot
to cold)
Entropy
: A measure of how energy and matter is
spread out (dispersed) among the atoms and
molecules of a system and its surroundings.
Free Energy
: A thermodynamic function that
relates enthalpy and entropy to spontaneity.
Thermodynamics:
Entropy and Free
Energy
Although heat (q) is a consideration in spontaneity, it is
not the only factor in its determination.
Dispersal of Energy
Statistical analysis of energy distribution of two quantized packets
of energy
Beige = Quantum of energy; Blue = No energy.
Note that energy is more likely to be distributed over
multiple particles (6 of 10) than concentrated on one .
Energy distribution of 4 particles with a total of 6
quantized units of energy.
Most probable configuration
is energy distributed over a
large number of particles
over a large number of
states.
As the number of particles and the number of
energy levels grows, one arrangement turns out to
be vastly more probable than the others.
Examples of Energy Dispersal
 Heat energy in a coffee cup being distributed to
the surroundings
 A rock rolling down a hill distributing its energy to
the air and hillside
Matter Dispersal
Probability of finding n molecules in
the original flask when the valve is
open is given by (1/2)
n
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Matter Dispersal and Energy Dispersal
Related to quantum mechanics
For larger n numbers (principal quantum number)
 Average radius increases
 Energy levels get closer together
Can be applied to macroscopic systems:
 n is related to the size of the system
For a vessel holding a sample of gas:
 Increase in size corresponds to an increase in n number
 Energy levels get closer together
 Since available energy has not changed, the number of ways of
distributing the total energy increases
When matter is dispersed into a larger volume,
energy is dispersed over more energy levels.
For gases at room temperature, the entropydriven
dispersal of matter is equivalent to an increase in
disorder of the system.
While dispersal of gases always increases disorder,
the same is not always true for solutions
Increase in disorder in the distribution of
potassium permanganate
Decrease in disorder in the
solvation of lithium hydroxide
Ludwig Boltzmann
S = k log W
S = Entropy of system
k = Boltzmann’s constant
W = Number or ways energy
can be distributed over the
available energy levels
Entropy
Thermodynamics:
Thermodynamics:
Determines
if
a process is
possible and spontaneous
and
the equilibrium state of the system (how far the reaction will
proceed)
Kinetics determines the rate of the process.
Review of Thermochemistry
For PressureVolume Work
Δ
E = q + P
Δ
V
Δ
E is the internal energy change of
the system
q
p
=
Δ
E  P
Δ
V
(at constant pressure)
q
p
= Enthalpy change =
Δ
H
(negative = exothermic; positive = endothermic)
Laws of Thermodynamics:
1
st
Law:
The energy of the universe is
constant (conservation law)
2
nd
Law:
The entropy of the universe is
always increasing
3
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 Fall '10
 Feebeck
 Thermodynamics, Energy, Entropy

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