control box in space and time. The control box is insulated, to be able to satisfy
thermodynamic conservation laws.
3.1 Thermodynamic Equilibrium
All macroscopic systems have “memory.” This memory is always with respect to
their stress-free state, which is the minimum energy state. All macroscopic systems
tend to evolve toward a minimum energy point, which is defined by intrinsic
properties. Evolution toward these minimum energy points can be slow or fast,
depending on external factors.
These minimum energy points of the system are called thermodynamic equilibrium states. These states usually are asymptotic states. Hence, they are static. Callen
(1985) provides a good description of thermodynamic equilibrium from the atomic
point of view: “The macroscopic thermodynamic equilibrium state is associated with
incessant and rapid transitions among all the atomic states consistent with the given
boundary conditions. If the transition mechanism among the atomic states is sufficiently effective, the system passes rapidly through all representative atomic states in
the course of a macroscopic observation; such a system is in thermodynamic
equilibrium. In actuality, few systems are in absolute and true thermodynamic
equilibrium. In absolute thermodynamic equilibrium, from the atomic point of
view, all radioactive materials would have decayed completely and nuclear reactions
would have transmuted all nuclei to the most stable of isotopes. Such processes,
would take cosmic times to complete, generally can be ignored. A system that has
completed the relevant [significant] processes of spontaneous evolution and that can
be described by a reasonable small number of parameters can be considered to be in
metastable thermodynamic equilibrium. Such a limited thermodynamic equilibrium
is sufficient for the application of thermodynamics.” This is the definition of
“thermodynamic equilibrium” we use in the rest of the book.
From a practical point of view, a system is considered to be in equilibrium if it
satisfies the laws of thermodynamics. However, this justification is actually circular.
That is to say, if a system satisfies the laws of thermodynamics, it is said to be in
equilibrium.
A succinct definition of thermodynamics with an example is given by Callen
(1985): “Thermodynamics is the determination of the equilibrium state that eventually results in a closed system.” (Fig. 3.1).
“Let us assume we have a container separated into two sections with a moveable rigid wall.
Container wall is assumed to be impermeable to matter, and adiabatic (heat does not enter or
leave the container). This container is the definition of closed system in thermodynamics.
Initially the separation wall is fixed. If we release the separation wall, it will move to a new
location due to gradient of pressure on each sides of the wall.
Then if we remove the adiabatic coating from the separation wall, the heat can freely flow
between two sections of the container. Now we drill holes in the separation wall, the matter
can flow freely between two sections depending on the concentration gradient. Every time a
constraint is removed, a spontaneous process will take place that will result in a new
74
3 Thermodynamics
thermodynamic conservation laws.
3.1 Thermodynamic Equilibrium
All macroscopic systems have “memory.” This memory is always with respect to
their stress-free state, which is the minimum energy state. All macroscopic systems
tend to evolve toward a minimum energy point, which is defined by intrinsic
properties. Evolution toward these minimum energy points can be slow or fast,
depending on external factors.
These minimum energy points of the system are called thermodynamic equilibrium states. These states usually are asymptotic states. Hence, they are static. Callen
(1985) provides a good description of thermodynamic equilibrium from the atomic
point of view: “The macroscopic thermodynamic equilibrium state is associated with
incessant and rapid transitions among all the atomic states consistent with the given
boundary conditions. If the transition mechanism among the atomic states is sufficiently effective, the system passes rapidly through all representative atomic states in
the course of a macroscopic observation; such a system is in thermodynamic
equilibrium. In actuality, few systems are in absolute and true thermodynamic
equilibrium. In absolute thermodynamic equilibrium, from the atomic point of
view, all radioactive materials would have decayed completely and nuclear reactions
would have transmuted all nuclei to the most stable of isotopes. Such processes,
would take cosmic times to complete, generally can be ignored. A system that has
completed the relevant [significant] processes of spontaneous evolution and that can
be described by a reasonable small number of parameters can be considered to be in
metastable thermodynamic equilibrium. Such a limited thermodynamic equilibrium
is sufficient for the application of thermodynamics.” This is the definition of
“thermodynamic equilibrium” we use in the rest of the book.
From a practical point of view, a system is considered to be in equilibrium if it
satisfies the laws of thermodynamics. However, this justification is actually circular.
That is to say, if a system satisfies the laws of thermodynamics, it is said to be in
equilibrium.
A succinct definition of thermodynamics with an example is given by Callen
(1985): “Thermodynamics is the determination of the equilibrium state that eventually results in a closed system.” (Fig. 3.1).
“Let us assume we have a container separated into two sections with a moveable rigid wall.
Container wall is assumed to be impermeable to matter, and adiabatic (heat does not enter or
leave the container). This container is the definition of closed system in thermodynamics.
Initially the separation wall is fixed. If we release the separation wall, it will move to a new
location due to gradient of pressure on each sides of the wall.
Then if we remove the adiabatic coating from the separation wall, the heat can freely flow
between two sections of the container. Now we drill holes in the separation wall, the matter
can flow freely between two sections depending on the concentration gradient. Every time a
constraint is removed, a spontaneous process will take place that will result in a new
74
3 Thermodynamics