THERMODYNAMICS

Thermodynamics is a branch of physics and of chemistry that studies the effects of changes in temperature, pressure, and volume on physical systems at the macroscopic scale by analysing the collective motion of their particles using statistics. Roughly, heat means "energy in transit" and dynamics relates to "movement"; thus, in essence thermodynamics studies the movement of energy and how energy instills movement. Historically, thermodynamics developed out of need to increase the efficiency of early steam engines.

The laws of thermodynamics:


Zeroth law of thermodynamics (stating that thermodynamic equilibrium is an equivalence relation):
If two thermodynamic systems are separately in thermal equilibrium with a third, they are also in thermal equilibrium with each other.
First law of thermodynamics (about the conservation of energy ):
The change in the internal energy of a closed thermodynamic system is equal to the sum of the amount of heat energy supplied to the system and the work done on the system.
Second law of thermodynamics, (about entropy) :
The total entropy of any isolated thermodynamic system tends to increase over time, approaching a maximum value.
Third law of thermodynamics( about absolute zero temperature):
As a system asymptotically approaches absolute zero of temperature all processes virtually cease and the entropy of the system asymptotically approaches a minimum value; also stated as: "the entropy of all systems and of all states of a system is zero at absolute zero" or equivalently "it is impossible to reach the absolute zero of temperature by any finite number of processes".
Onsager reciprocal relations (sometimes called the Fourth Law of Thermodynamics) :
Express the equality of certain relations between flows and forces in thermodynamic systems out of equilibrium, but where a notion of local equilibrium exists.

Typical thermodynamic system, showing input from a heat source (boiler) on the left and output to a heat sink (condenser) on the right. Work is extracted, in this case by a series of pistons.

In thermodynamics, a thermodynamic system, originally called a working substance, is defined as that part of the universe that is under consideration. A real or imaginary boundary separates the system from the rest of the universe, which is referred to as the environment or surroundings(sometimes called a reservoir). A useful classification of thermodynamic systems is based on the nature of the boundary and the quantities flowing through it, such as matter, energy, work, heat, and entropy. A system can be anything, for example a piston, a solution in a test tube, a living organism, a planet, etc.

THERMODYNAMIC SYSTEM