Lecture 3:
Intro to Entropy
• Reading: Zumdahl 10.1, 10.3
• Outline:
– Why enthalpy isn’t enough.
– Statistical interpretation of entropy
– Boltzmann’s Formula
Enthalpy and Spontaneous Rxns
• Early on in the development of
thermodynamics, it was believed that if a
reaction was exothermic, it was
spontaneous.
• Consider the following reaction:
H
2
O(s)
H
2
O(l)
∆
H°
rxn
= +6.02 kJ
• Endothermic….
.yet spontaneous!
Enthalpy and Spontaneous Rxns
• Consider the following problem:
Mixing of
a gas inside a bulb adiabatically (q = 0).
• q = 0, w = 0,
∆
E = 0,
and
∆
H = 0
….but it still happens
Statistical Interpretation of
Entropy
• Imagine that we have a collection of 3
distinguishable particles who have a total
energy of 3
ε
.
• Let’s ask the question, “How will this fixed
amount of energy distribute itself over the
particles?”
Statistics and Entropy (cont.)
• Our system
consists of
three distinguishable
particles.
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 Winter '10
 Stiban,F
 Thermodynamics, Statistical Mechanics, Entropy, #

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