Enthalpy
In order to facilitate the calculation of various thermodynamic processes, the
concept of enthalpy was introduced by U. Gibbs.
Enthalpy (Greek - enthalro - to heat) is a state function of a system, denoted by the
letter H.
The sum of the internal energy of the system with U, the sum of the pressure of the
system P multiplied by the volume of the system V plays an important role in various
thermodynamic
calculations; this quantity is called enthalpy.
H=U+PV.
(4.19)
Entropy
Entropy (Greek, entroria - rotation, change) is a state function of a thermodynamic
system.
Entropy represents the direction of the process of mutual heat exchange between the
thermodynamic system and the external environment.
We describe the curve of voluntary process I-II in Ts-diagram.(4.36) in the reverse
process from :
Eqdq=Tds
(4.37)
it follows that
So, the amount of heat received (or given) by the system in the reverse
processisrepresented by the surface under
the process curve in the
diagram Ts.
The convenience of the Ts-diagram is that the
amount of heat supplied
and removed from the cycle, as well as the work obtained as a result of
the cycle (or the work expended if the cycle is reversed), are clearly
depicted on it.
c
9. 2 Law of thermodynamics.
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