PlanetPhysics/Thermodynamics an Introduction and Definitions

[[../Thermodynamics/|Thermodynamics]] is the science of the flow of [[../Heat/|heat]]. It applies to macroscopic [[../SimilarityAndAnalogousSystemsDynamicAdjointnessAndTopologicalEquivalence/|systems]] in [[../ThermalEquilibrium/|equilibrium]] and how to go from one equilibrium state to another. It is entirely empirical and summed up into four laws and basic mathematics.

[[../ZerothLawOfThermodynamics/|Zeroth law of thermodynamics]]: defines [[../BoltzmannConstant/|temperature]] $T$

[[../FirstLawOfThermodynamics/|First law of thermodynamics]]: defines [[../CosmologicalConstant/|energy]] $U$

Second law of Thermodynamics: defines [[../ThermodynamicLaws/|entropy]] $S$

[[../BoltzmannConstant/|Third Law of Thermodynamics]]: gives numerical value to entropy $S$

These laws are UNIVERSALLY VALID and cannot be circumvented.

Definitions used in Thermodynamics:

• System : The part of the [[../MultiVerses/|Universe]] that we choose to study
• Surroundings : The rest of the Universe
• [[../GenericityInOpenSystems/|boundary]]: The surface dividing the System from the Surroundings
• Homogeneous : A single phase is in the system
• Hetrogeneous : Different phases are in the system

Examples of systems:

• A person
• Hot coffee in a thermos
• [[../LongRangeCoupling/|glass]] of ice water
• [[../Volume/|volume]] of 4 liters of air in a room

whatever is left over is the surroundings. Between the system and the surroundings is the boundary.

Examples of boundaries:

• Real like the outside of a person's skin
• The inner wall of the thermos
• An imaginary boundary surrounding the 4 liters of air

Systems can be:

• Open : [[../CosmologicalConstant/|mass]] and Energy can transfer between the System and the Surroundings
• Closed : Energy can transfer between the System and the Surroundings, but not mass
• Isolated : Neither Mass nor Energy can transfer between the System and the Surroundings

Describing Systems requires:

• A few macroscopic properties: p, T, V, n, m, etc.
• Knowledge if System is Homogeneous or Hetrogeneous
• Knowledge if System is in Equilibrium State
• Knowledge of the number of components

Two classes of Properties:

• Extensive : Depend on the size of the system (n,m,V,...)
• Intensive : Independent of the size of the system (T, p, $\overline{V}=\frac{V}{n}$,...)

A system is in equilibrium if the properties that describe the system, such as $P$, $T$, $V$, etc. do not change in time or space. A gas in a container needs to be the same $P$, $T$, $V$ to be in equilibrium.

References

This is a derivative [[../Work/|work]] from [1] a Creative Commons Attribution-Noncommercial-Share Alike 3.0 work

[1] MIT OpenCourseWare, 5.60 Thermodynamics and Kinetics: Thermodynamics and Kinetics, Spring 2008