A thermodynamic process may be defined as the energetic evolution of a
thermodynamic system proceeding from an initial state to a final state.
Paths through the space of thermodynamic variables are often specified by
holding certain thermodynamic variables constant.
The pressure-volume
conjugate pair is concerned with the transfer of mechanical or dynamic
energy as the result of work.
* An isobaric process occurs at
constant pressure. An example would be to have a movable piston in a
cylinder, so that the pressure inside the cylinder is always at
atmospheric pressure, although it is isolated from the atmosphere. In
other words, the system is dynamically connected, by a movable boundary,
to a constant-pressure reservoir.
* An isochoric process is one
in which the volume is held constant, meaning that the work done by the
system will be zero. It follows that, for the simple system of two
dimensions, any heat energy transferred to the system externally will be
absorbed as internal energy. An isochoric process is also known as an
isometric process or an isovolumetric process. An example would be to
place a closed tin can containing only air into a fire. To a first
approximation, the can will not expand, and the only change will be that
the gas gains internal energy, as evidenced by its increase in temperature
and pressure. Mathematically, ?Q = dU. We may say that the system is
dynamically insulated, by a rigid boundary, from the environment.
The
temperature-entropy conjugate pair is concerned with the transfer of
thermal energy as the result of heating.
* An isothermal
process occurs at a constant temperature. An example would be to have a
system immersed in a large constant-temperature bath. Any work energy
performed by the system will be lost to the bath, but its temperature will
remain constant. In other words, the system is thermally connected, by a
thermally conductive boundary to a constant-temperature reservoir.
* An adiabatic process is a process in which there is no energy added or
subtracted from the system by heating or cooling. For a reversible
process, this is identical to an isentropic process. We may say that the
system is thermally insulated from its environment and that its boundary
is a thermal insulator. If a system has an entropy which has not yet
reached its maximum equilibrium value, the entropy will increase even
though the system is thermally insulated.
The following let you
play with different processes:
The work done, heat transfer, internal
energy as well as entropy change will be shown when you change parameter
with slider bar.