  In the extended phase space, a general method is used to derive all the
possible adiabatic processes for charged AdS black hole. Two kinds are found,
one is zero temperature adiabatic process which is irreversible, the other is
isochore adiabatic process which is reversible. For the zero temperature
adiabatic expansion process, entropy is increasing; pressure, enthalpy, Gibbs
free energy and internal energy are decreasing; system's potential energy is
transformed to the work done by the system to the outer system. For the
isochore adiabatic process, entropy and internal energy are fixed; temperature,
enthalpy and Gibbs free energy are proportional to pressure; during the
pressure increasing process, temperature is increasing and system's potential
energy is transformed to its kinetic energy. Comparing these two adiabatic
processes with those in normal thermodynamic system, we find that the zero
temperature adiabatic process is much like the adiabatic throttling
process(both are irreversible and with work done), the isochore adiabatic
process is much like a combination of the reversible adiabatic process (both
with fixed entropy) and the adiabatic free expansion process (both with fixed
internal energy).
