Chapter 10 Study Guide
The first law of thermodynamics: The energy of the universe is constant
A process is spontaneous if it occurs without outside intervention.
Thermodynamics tells us the direction of a process but NOT the speed(rate).
Spontaneous process:
a process that occurs without outside intervention
The change in the entropy of the universe for a given process is a measure of the force behind that
process.
Spontaneous does not mean fast
Entropy (
S
):
a thermodynamic function that measures randomness or disorder
Nature spontaneously proceeds toward the states that have the highest probabilities of existing.
The probability of occurrence of a particular arrangement (state) depends on the number of ways
(microstates) in which that arrangement can be achieved.
Positional probability:
a type of probability that depends on the number of arrangements in space that
yield a particular state
Isothermal process:
a process in which the temperature remains constant
In an isothermal process involving a gas ∆E=0 because the energy of an ideal gas can be changed
only by changing the temperature. Since
∆E = q + w
q = w
Free expansion: one step expansion—no work
P
external
(the pressure against which the gas expands) is zero in a free expansion
The external pressure is always almost exactly equal to the pressure produced by the gas.
w
rev
= nRT
ln(
V
2
/V
1
)
q
rev
=  w
rev
= nRT
ln(
V
2
/V
1
)
Only when the expansion & compression
are both done reversibly
(by an infinite number of steps) is
the universe the same after the cyclic process (the expansion and the subsequent compression of the
gas back to its original state).
All real processes are irreversible
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 Fall '09
 Therien
 Thermodynamics, Entropy, qrev

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