Introduction and Definitions First of all is need to understand that thermodynamics is the study of the stable equilibrium in macroscopic system but what’s stable equilibrium and macroscopic system ?
Macroscopic system:
For a system constituted of N particles, N>>N‾‾√. Fluctuations must be small compared to mean, and this can happen only for large particle numbers.
Stable Equilibrium:
This occurs when all the macroscopic observables for some systems are constant. There is not new mass energy flow, and the system returns to the initial state.
General Definitions
Simple system: an special and homogeneous system.
Constrains: This refers to the walls that form part of the system they can be permeable or impermeable, adiabatic or diathermy.
The mail task of thermodynamics is to calculate equilibrium states when a constrain is remove and it is relate to all the macroscopic variables.
Composite systems: This is a system composed by some subsystems separated by by constrains.
Simple system: When a system is composed of sub-systems but separated by constrains.
Close system: A system all of whose macroscopic observable as mass, energy, volumen or mole numbers.
Isolated system: A system surrounded by an impeccable wall. There isn’t mass or energy flow.
Open system: A system where there is an exchange of mass and energy.