Ideals are simple and able to be easily understood but never exist in reality. In this book a
theory based on the second law of thermodynamics and its applications are described. In
thermodynamics there is a concept of an ideal gas which satisfies a mathematical formula PV =
RT. This formula can appro- mately be applied to the real gas so far as the gas has not an
especially high pressure and low temperature. In connection with the second law of thermo-
namics there is also a concept of reversible and irreversible processes. The reversible process
is a phenomenon proceeding at an infinitely low velocity while the irreversible process is
that proceeding with a finite velocity. Such a process with an infinitely slow velocity can
really never take place and all processes observed are always irreversible therefore the
reversible process is an ideal process while the irreversible process is a real process.
According to the first law of thermodynamics the energy increase dU of the thermodynamic system
is a sum of the heat dQ added to the system and work dW done in the system. Practically
however the mathematical formula of the law is often expressed by the equation or some
similar equations derived from this formula is applied to many phenomena. Such formulae are
however th- retically only applicable to phenomena proceeding at an infinitely low velocity
that is reversible processes or ideal processes.
