Download What is Thermodynamics?

Major Concepts
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System / Surroundings
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Open / Closed / Isolated
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Microscopic connection to Internal Energy
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Thermal motion
Boltzmann distribution
First Law of Thermodynamics
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Internal energy, U = U(T, V, n)
Heat, q
Work, w
Changes in Work (by vs. on the system!)
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Under free expansion
At constant pressure
Under a reversible condition
Along an isothermal reversible path
various
thermodynaimc
paths
What is Thermodynamics?
• The study of the transformation of energy (Atkins).
• An operational science concerned with macroscopic properties that,
at least in principle, can be measured.
What are the Goals of Thermodynamics?
• Predict what type of chemical and physical processes are possible,
and under what conditions.
• Calculate quantitatively the properties of the equilibrium state that
ensures when a process is carried out.
Important Limitation of Thermodynamics:
• Although thermodynamics tells us which processes will occur
spontaneously, it does not tell us how rapidly they will occur.
Thermodynamics Terminology
Thermodynamic Universe:
System + Surroundings
Surroundings: The portion of the physical world (outside the system)
that can exchange matter and/or energy with the
system
Systems:
Open
Closed
Isolated
Thermodynamics Terminology
Thermodynamic State is defined by specifying a set of
measurable properties sufficient so that all remaining properties
are determined.
These properties are called state functions.
Properties:
Extensive
V, M, U, N, …
Thermodynamic Equilibrium =
mechanical
+
thermal
+
chemical
Intensive
T, P, C, …
Thermodynamic Terminology
A (thermodynamic) process changes the (thermodynamic)
state of the system.
P
U  U f  U i
V
Changes in the values of all state function are independent on
the path via which the change occurs.
A reversible process is one where the whole series of changes
can be reversed such that the original condition is restored.
P
Reversibility is an ideal limit.
Processes:
isothermal,
isobaric,
adiabatic, …
V
Thermodynamics Terminology
• Internal Energy is the total energy of a system (kinetic +
potential):
U=K+P
• Heat is energy transferred due to temperature differences only.
Heat can be
− released (exothermic process) or
− absorbed (endothermic process).
• Work is also a form of energy “in transit”.
Work is caused by the action of a force.
− Work done by a system decreases the internal energy.
− Work done on a system increases the internal energy.
• Heat and work are not functions of state: they depend on the
path via which the change occurs.
Varieties of Work
The variables involved in work form conjugate pairs of
intensive and extensive variables
external work:
on the system
First Law of Thermodynamics
• Energy is conserved.
Thus, internal energy can be changed by heat and work:
U=q + w,
or in differential form
dU=dq + dw
• One cannot construct a machine which runs indefinitely
without fuel.
• The quantity “heat plus work” (q+w) is a state function, i.e., is
independent of the path between the initial and final states.
• In the adiabatic process (q=0) the work is independent of the
path between the initial and final states.