Thermodynamics

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Thermodynamics

• Thermodynamic system. First and second laws of
  thermodynamics.

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Epilog
"A theory is the more impressive the greater the
simplicity of its premises, the more different
are the kinds of things it relates, and the more
extended is the range of its applicability.
Therefore, the deep impression which classical
thermodynamics made upon me. It is the only
physical theory of universal content which I am
convinced, that within the framework of
applicability of its basic concepts, will never
be overthrown" Albert Einstein.
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Goal and method of thermodynamics
A goal of equilibrium thermodynamics is given a
system in a well-defined initial state, subject
to accurately specified constraints, to calculate
what the state of the system will be once it has
reached equilibrium. Thermodynamic description
offers simpler picture of system composed of
enormous number of particles each having at least
3 degrees of freedom, i.e. replaces direct
analysis of those innumerable degrees of freedom
with a few macroscopic system parameters.
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Thermodynamic system
System - is part of the world selected for
consideration. The region outside the system is
called surroundings. The surface separating
system from surroundings is called boundary
All interactions of the system with its
surroundings must occur through the boundary.
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Classification of systems
if all deformation occur faster then heat
transfer neglecting heat loss due to thermal
conductivity of flask
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Variables of state
In thermodynamics any system is described by a
small number of variables of state or properties.
A characteristic of a system is called a variable
of state only if its value does not depend on how
the system is brought to the chosen conditions.
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Extensive and Intensive properties
Imagine a system is arbitrarily split in two
parts. Some properties such as temperature,
density and component concentration will not
change - these properties are called intensive.
Others, such as volume and mass will change
corresponding to size each part - these
properties are called extensive.
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Thermodynamic equilibrium
A system is said to be in a state of
thermodynamic equilibrium if its intensive
parameters are homogeneous within the system's
boundary and do not change with time. Global
thermodynamic equilibrium (GTE) means that those
intensive parameters are homogeneous throughout
the whole system and time, while local
thermodynamic equilibrium Local thermodynamic
equilibrium (LTE) means that those intensive
parameters are varying in space and time, but are
varying so slowly that for any point, one can
assume thermodynamic equilibrium in some
neighborhood about that point.
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Interactions of system surroundings
All interactions of the system with its
surroundings must occur through the boundary.
Two types of things can pass the
boundary matter and energy. Energy comes in two
forms - work and heat.
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Work
Work energy transfer occurring via ordered
change of some system parameter. Mechanical
work Work force x distance dW Fds For
force generated by pressure dW -PextdV,
where Pext - external pressure, dV - change of
system volume. since Pext F/S -dV Ads,
where A - the area force F is applied to.
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Heat
Heat is also related to motion (example below)
but still it is quite different from work
Benjamin Thomsons cannon-boring experiment. It
is hardly necessary to add, that anything which
any insulated body can continue to furnish
without limitation, cannot possibly be a material
substance and it appears to me to be extremely
difficult, if not quite impossible, to form any
distinct idea of anything capable of being
excited and communicated in the manner the Heat
was excited and communicated in these
experiments, except it be Motion.
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Brownian motion
In 1827 British botanist Robert Brown observed
minute particles within vacuoles in the pollen
grains executing a jittery motion. He then
observed the same motion in particles of dust,
enabling him to rule out the hypothesis that the
motion was due to pollen being alive. Although
he himself did not provide a theory to explain
the motion, the phenomenon is now known as
Brownian motion in his honor. In 1905 Albert
Einstein invented a theory explaining brownian
motion due to many random collisions of suspended
particles with molecules making up the
solution Brownian Motion Applet
Albert Einstein In 1905
Robert Brown
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Temperature
Degree of hotness temperature is an intuitive
parameter so far Relative temperature
scales 1701 - Ole Romer, Danish astronomer,
introduced one of the first temperature scales
where he accepted temperature of mixture of ice
and concentrated salt solution as 0 oR and
temperature of boiling water as 60 oR 1724 -
Gabriel Fahrenheit, German physicist and
engineer, proposed another scale that used same
temperature for 0 oF, but temperature of healthy
horse (according to one legend) as 100 oF - new
scale had finer gradations then that by Romer, so
at Fahrenheit scale water freezes as 32 oF and
boils at 212 oF 1742 - Anders Celsius, Swedish
astronomer, proposed his temperature scale where
the boiling point of water at 1,000 millibar was
defined as 0 degrees and the freezing point of
water was defined as 100 degrees. After Celsius
died, the maker of thermometers with Celsius
scale brought the scale to the familiar
direction.
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Temperature... (cont)
Relative temperature scales (cont) 1954 -
Celsius scale redefined 0.01 oC - triple point
of water, 1 oC 1/273.16 (the difference in
temperature between the triple point of water and
absolute zero) Absolute temperature
scales 1850's Kelvin scale introduced by William
Thomson, 1st baron Kelvin as an absolute scale
tied to the Celsius scale (so that 1 K increment
will correspond to 1 oC increment 1859 -
Rankine scale. Introduced by Scottish engineer
William John Macquorn Rankine. Absolute scale
analogous to Kelvin's but value of 1 degree
increment was tied to 1 oF
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Heat work
Heat and work both represent transient energy,
intuitively, there must be some sort of
equivalence between the two. Hopefully,
Thomsons cannon experiment had convinced you that
heat in essence is a product of motion. And yet
we can already see difference between these two
forms of energy work is a result of directed
motion, while we do not observe any (at least
directed) motion in hot objects. Can we convert
work to heat and heat to work without restriction?
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Fundament of thermodynamics(First and Second
Laws)
Thermodynamic theory is based on two fundamental
Laws that are known from experience. These Laws
are not to be proven but rather are taken for
granted First Law describes energetic
equivalence of work and heat. Second Law defines
direction of spontaneous process and answers
questions of extent of possibility to
interconvert heat and work.
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First Law of Thermodynamics
First Law of Thermodynamics is a statement of
Conservation of Energy. dE dQ dW The
increase in the internal energy of a system is
equal to the amount of energy added to the system
by heating, plus the amount added in the form of
work done on the system. Notice that dQ is
positive when heat is added to the system and dW
is positive when work is done on the system. This
is chemists system-centric definition. In
engineering, work done by the system is
considered more important, so the sign before
used by engineers dW is negative.
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Second Law of Thermodynamics

• Second Law of thermodynamics defines the
  direction of a spontaneous process.
• hot cup of coffee in the office will eventually
  get cold
• the car stops when the brakes are applied
• Both of those things happen spontaneously. Why
  wouldn't the reverse also take place
  spontaneously?
• Why would not the car start moving at the expense
  of cooling breaks or coffee get hot by borrowing
  heat from room temperature air?
• Notice that the reverse process would not violate
  the First Law. There must be some other principle
  defining direction of a spontaneous process for
  an isolated system.
• We need another principle independent on the
  First Law.

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Second Law of Thermodynamics
Lets take the spontaneously cooling coffee fact
for granted and make a Law out of it It would
sound something like "It is impossible for the
system to operate in such a way that sole result
is the transfer of heat from a cold to a hot
object." (Clausius Statement) Second statement
(equivalent to the one above) "It is impossible
for a system that operates in a cycle to generate
work while transferring heat from a single
reservoir." (Kelvin-Planck Statement) The two
statements above are equivalent formulations of
the Second Law of Thermodynamics.
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Corollaries of the Second Law

• Second Law said in the above statements gives us
• defined direction of spontaneous process
• upper limit on anyone's ability to convert heat
  into work
• definition of absolute temperature
• definition of entropy as a new state function
• suggests interesting properties of entropy for
  systems not in the state of equilibrium
• We will derive these corollaries in the next
  lecture.