This preview shows pages 1–3. Sign up to view the full content.
Lecture 12:
Entropy
We have found that entropy is a state variable (associated with equilibrium states
of the system) and its change
Δ
S
can be calculated along any reversible path.
We have also obtained the
Clausius inequality:
It allows us to decide whether a process associated with the flow of heat
δ
q
is
irreversible and spontaneous
,
reversible
or
nonspontaneous.
Example: Consider n moles of ideal gas isothermally expanded from V
0
to cV
0
.
(dU=0=
δ
w+
δ
q):
If the initial and final states are the same, but the
external pressure is fixed
P=P
0
/c
(irreversible and spontaneous process), we get
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document We also have to consider
the entropy change of the surroundings,
Δ
S
surr
.
If the
total entropy:
the process is
irreversible
the process is
reversible
the process is
nonspontaneous
In the previous example, heat was taken isothermally and reversibly from
the surroundings, so we get
In the expansion against constant pressure (extraction of heat is almost reversible),
we obtain
Essentially, you can see that we study:
system
This is the end of the preview. Sign up
to
access the rest of the document.
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

Click to edit the document details