States And Thermodynamic Processes. General Principle.
The thermodynamics study the
physical processes which take place in large particles number
systems, wherein interfere thermic phenomenon situations. A
thermodynamics system is a random portion of Universe which may
interact with the surrounding medium (the exterior). A system is
called isolated in case this one cannot interact with outside
ambience. An enclosed system exchanges only energy with the exterior.
A system is opened in case this one exchanges substances with the
outside medium.
The state of a thermodynamics system
at a certain time is determined by a finite number of state
parameters. The pressing and volume are mechanical parameters, while
the temperature is one specific to thermodynamic systems. The
intensive parameters as pressure, temperature, concentration,
electric tension, etc. do not depend on the number of particles in
the system, having the same value for all the elements of the system.
The extensive parameters as volume, internal energy, entropy,
electric charge, etc. are proportional with the number of particles
in the system, being additive measures.
To express the elementary mechanical
work, we associate to each contact a pair of parameters form the
system and exterior, ones of force, others of position (e.g. :
pressure and volume). The thermodynamic balance state is a state
wherein state parameters are constant through time and there are no
fluxes inside the system. The general principle of thermodynamics
shows that an isolated thermodynamics system is at a moment
disturbed, then after the disturbance cessation, the system
spontaneously evolves to a thermodynamic balance state it reaches
after a time T, named rest time. The system can never be disturbed by
itself.
Temperature. The Zero Principle of Thermodynamics.
Temperature. The Zero Principle of Thermodynamics.
Two thermodynamic systems in contact
make a global system which in time reaches the thermic balance state.
The balance does not break in case we remove the contact between
systems and after a while we reconnect these. It shows that the
global system is in state of balance, then each component system will
be in thermic balance itself. From here is deduced the third
principle of thermodynamics, the zero principle, or the law of
thermic balance transitivity: two systems in balance with the third
are between in balance.
This experimental law allows the
introduction of temperature as macroscopic parameter, a common
feature of the systems in balance. The zero principle of
thermodynamics can be rephrased with the help of temperature notion:
there is a state function named temperature; the equality of the
temperatures in all the spots is the thermic balance condition for
the two thermodynamic systems or two parts of the same system. Since
the objects in thermic balance have the same temperature, it is
possible to measure their temperature using a thermometer, which is
in thermic balance with these. As thermometric object can be any item
with measurable property that varies with temperature in reproductive
way. For the appreciation of temperature we can choose: volume
variation, pressure variation, electric resistance variation, etc.
