Thermodynamics of open biological environments.

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Thermodynamics of open biological environments.
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Heat and Thermodynamics

• First Law of Thermodynamics
• Second Law of Thermodynamics
• Entropy
• Adiabatic Process
• Heat Engine Cycle
• Enthalpy

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First Law of Thermodynamics

• The first law of thermodynamics is the
  application of the conservation of energy
  principle to heat and thermodynamic processes

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• The first law makes use of the key concepts of
  internal energy, heat , and system work. It is
  used extensively in the discussion of heat
  engines .

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System Work

• When work is done by a thermodynamic system, it
  is ususlly a gas that is doing the work. The work
  done by a gas at constant pressure is

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For non-constant pressure, the work can be
visualized as the area under the pressure-volume
curve which represents the process taking place.
The more general expression for work done is

• Work done by a system decreases the internal
  energyof the system, as indicated in the First
  Law of Thermodynamics. System work is a major
  focus in the discussion of heat engines.

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Second Law of Thermodynamics

• The second law of thermodynamics is a general
  principle which places constraints upon the
  direction of heat transfer and the attainable
  efficiencies of heat engines . In so doing, it
  goes beyond the limitations imposed by the first
  law of thermodynamics. It's implications may be
  visualized in terms of the waterfall analogy.

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Second Law Heat Engines

• Second Law of Thermodynamics It is impossible to
  extract an amount of heat QH from a hot reservoir
  and use it all to do work W . Some amount of heat
  QC must be exhausted to a cold reservoir. This
  precludes a perfect heat engine .
• This is sometimes called the "first form" of the
  second law, and is referred to as the
  Kelvin-Planck statement of the second law.

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Second Law Refrigerator

• Second Law of Thermodynamics It is not possible
  for heat to flow from a colder body to a warmer
  body without any work having been done to
  accomplish this flow. Energy will not flow
  spontaneously from a low temperature object to a
  higher temperature object. This precludes a
  perfect refrigerator . The statements about
  refrigerators apply to air conditioners and heat
  pumps , which embody the same principles.

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Entropy

• Second Law of Thermodynamics In any cyclic
  process the entropy will either increase or
  remain the same.
• Entropy a state variable whose change is
  defined for a reversible process at T where Q is
  the heat absorbed.

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• Entropya measure of the amount of energy which
  is unavailable to do work.
• Entropy a measure of the disorder of a system.
  Entropy a measure of the multiplicity of a
  system.

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• Entropy in Terms of Heat and Temperature
• The macroscopic relationship which was originally
  used to define entropy S is
• dS Q/T
• This is often a sufficient definition of entropy
  if you don't need to know about the microscopic
  details.

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• Since entropy gives information about the
  evolution of an isolated system with time, it is
  said to give us the direction of "time's arrow "
  . If snapshots of a system at two different times
  shows one state which is more disordered, then it
  could be implied that this state came later in
  time. For an isolated system, the natural course
  of events takes the system to a more disordered
  (higher entropy) state.

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• Alternative statements Second Law of
  Thermodynamics
• Biological systems are highly ordered how does
  that square with entropy?

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Adiabatic Process

• An adiabatic process is one in which no heat is
  gained or lost by the system. The first law of
  thermodynamics with Q0 shows that all the change
  in internal energy is in the form of work done.
  This puts a constraint on the heat engine process
  leading to the adiabatic condition shown below.
  This condition can be used to derive the
  expression for the work done during an adiabatic
  process.

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• The ratio of the specific heats g CP/CV is a
  factor in determining the speed of sound in a gas
  and other adiabatic processes as well as this
  application to heat engines. This ratio g 1.66
  for an ideal monoatomic gas and g 1.4 for air,
  which is predominantly a diatomic gas.

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Heat Transfer

• The transfer of heat is normally from a high
  temperature object to a lower temperature object.
  Heat transfer changes the internal energy of both
  systems involved according to the First Law of
  Thermodynamics.

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Heat Conduction

• Conduction is heat transfer by means of molecular
  agitation within a material without any motion of
  the material as a whole. If one end of a metal
  rod is at a higher temperature, then energy will
  be transferred down the rod toward the colder end
  because the higher speed particles will collide
  with the slower ones with a net transfer of
  energy to the slower ones. For heat transfer
  between two plane surfaces, such as heat loss
  through the wall of a house, the rate of
  conduction heat transfer is

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• Q heat transferred in time t
• T thermal conductivity of the barrier
• A area
• d thickness of barrier

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Heat Convection

• Convection is heat transfer by mass motion of a
  fluid such as air or water when the heated fluid
  is caused to move away from the source of heat,
  carrying energy with it. Convection above a hot
  surface occurs because hot air expands, becomes
  less dense, and rises (see Ideal Gas Law).

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• Hot water is likewise less dense than cold water
  and rises, causing convection currents which
  transport energy. Convection is thought to play a
  major role in transporting energy from the center
  of the Sun to the surface, and in movements of
  the hot magma beneath the surface of the earth

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• It is difficult to quantify the effects of
  convection since it inherently depends upon small
  nonuniformities in an otherwise fairly
  homogeneous medium. In modeling things like the
  cooling of the human body, we usually just lump
  it in with conductio

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Heat Engines

• A heat engine typically uses energy provided in
  the form of heat to do work and then exhausts the
  heat which cannot be used to do work.
  Thermodynamics is the study of the relationships
  between heat and work. The first law and second
  law of thermodynamics constrain the operation of
  a heat engine.

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• The first law is the application of conservation
  of energy to the system, and the second sets
  limits on the possible efficiency of the machine
  and determines the direction of energy flow.

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Enthalpy

• Four quantities called "thermodynamic
  potentials" are useful in the chemical
  thermodynamics of reactions and non-cyclic
  processes. They are internal energy, the
  enthalpy, the Helmholtz free energy and the Gibbs
  free energy. Enthalpy is defined by

H U PV
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• where P and V are the pressure and volume, and U
  is internal energy. Enthalpy is then a precisely
  measurable state variable, since it is defined in
  terms of three other precisely definable state
  variables. It is somewhat parallel to the first
  law of thermodynamics fora constant pressure
  system
• Q DU PDV
• since in this case QDH

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• It is a useful quantity for tracking chemical
  reactions. If as a result of an exothermic
  reaction some energy is released to a system, it
  has to show up in some measurable form in terms
  of the state variables. An increase in the
  enthalpy H U PV might be associated with an
  increase in internal energy which could be
  measured by calorimetry, or with work done by the
  system, or a combination of the two.

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• The internal energy U might be thought of as the
  energy required to create a system in the absence
  of changes in temperature or volume. But if the
  process changes the volume, as in a chemical
  reaction which produces a gaseous product, then
  work must be done to produce the change in
  volume. For a constant pressure process the work
  you must do to produce a volume change DV is PDV.
  Then the term PV can be interpreted as the work
  you must do to "create room" for the system if
  you presume it started at zero volume.

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