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Notes 11
Chemical reactions
The concept of equilibrium can be applied to a description of chemical reactions. A
simple example is the formation of H2O from H2 and O2
2H2 + O2 2H2O
In this reaction
dnH2 : dnO2 : dnH2O = 2, 1, +2
at equilibrium
(dG)T,P =
1
Entropy of mixing
Looking again at the entropy change in an adiabatic free expansion (see Notes 5
pg. 7)
Gas
Vacuum
Gas
The entropy change in this process is
S = nR ln (Vf / Vi)
Then, with Vf = 2Vi,
S = nR ln 2 = Nk ln 2
and the information required to
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STATISTICAL THERMODYNAMICS
Statistical thermodynamics (SM) is the formalism that enables a connection
between the quantum properties of the components of a system and the
macroscopic properties of this system.
We define the macrostate (or configuration)
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Notes 1
THERMAL PHYSICS
Walter W. Duley
The study of the macroscopic properties of matter specifically related to
temperature
Classical thermodynamics;
Describes the macroscopic properties of matter without consideration
of individual atoms and molecule
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Notes 7
Kinetic theory of gases
The properties of gases can be calculated from first principles using a simple
kinetic theory and after making several assumptions. These are:
All samples contain a large number of atoms
These atoms move along ballistic t
1
Taking
Ni = gi exp ( i) = N
= N / (gi exp ( i) ) = N / Z
where Z is called the partition function.
The partition function is a sum over all states, weighted according to each
states Boltzmann factor. For a classical system, once Z is determined, all
o
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Notes 3
HEAT CAPACITY
The term heat capacity is a measure of the ability of a substance to store
internal energy. Internal energy can be stored in a variety of ways;
Motion of atoms/molecules (KE)
Rotation of atoms/molecules
Motion of electrons in a met
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Notes 5
Entropy and available energy
Only some fraction of the energy Q extracted from a body can be used to
perform work. For a Carnot (ie. ideal) engine operating between
temperatures TH and TL
dQrev [1 TL/TH] = dWrev
is the work performed for dQrev e
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Notes 2
Once a set of basic state variables (P, V, T) have been defined, these can be used to
develop a number of other useful parameters.
EXPANSION AND COMPRESSION
The isothermal compressibility, , is defined as
= 1 (V /P)T
V
(Pa-1)
and the volume exp
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Notes 4
While engines and refrigerators can operate on many different types of cycle
the most efficient cycle is based on two isotherms and two adiabats. This is
the Carnot Cycle.
GENERALIZED CARNOT CYCLES
The Carnot cycle is a generic series of process
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Notes 6
Enthalpy: Joule Thomson expansion
In a JT (or throttling) expansion, a sample of gas undergoes an adiabatic
expansion from (Pi, Vi) to (Pf, Tf). Then
Uf Ui = W + Q = W
since Q = 0.
The work, W, arises from two terms: the work done on the gas by