Thermodynamics

I have spent a great deal of time attempting understand Thermo. Not just to be able to answer questions in an exam, but to really get to grips with Thermodynamics and not be intimidated by the many subtleties, tricks and assumptions which permeate the field.

I should say that I’m going to be talking about the fundamentals of Engineering Thermodynamics. There may be occasional forays into Statistical Mechanics, Mathematics or Materials Science, but my interest is centred on making effective models which can be used to design or analyse machines which convert Heat into Work.

A tutor of mine at college told his class this hardly-inspiring quotation:

“Thermodynamics is a funny subject. The first time you go through it, you
don’t understand it at all. The second time you go through it, you think
you understand it, except for one or two small points. The third time you
go through it, you know you don’t understand it, but by that time you are
used to it, so it doesn’t bother you any more.”
Arnold Sommerfeld, making excuses

(The Tutor was one of a collection of people who were intellectually gifted, bad teachers. Had any bothered to think about the difficulties their students faced, this blog would probably have been unnecessary -at least for me).

If you are struggling to understand Thermo, and sick of applying formulae you don’t really understand, then I hope that this work will be useful. There are currently 35 small articles in the pipeline which will address inherently confusing topics and those which are often just poorly explained. Each piece will consist of a blog post which acts as very brief commentary on various pngs embedded in the post.

This material is provided free. If you’d like to access the full set of my notes (over 100 such posts) then simply contact me for pricing. I’m also available to provide online tutoring for those who want additional explanation (perhaps in the run-up to final exams).


1.  Why I think Thermodynamics is hard


2.  State postulate


3.  Gibb’s phase rule


4.  Zeroth law


5.  State property vs path dependent variable


6.  Quasi-static (or quasi-equilibrium) processes


7.  Particle speed distribution in a gas (1)


8.  Particle speed distribution in a gas (2)


9.  Entropy intuition via microstates


10.  System temperature affects entropy


11.  Microstates and equilibrium


12.  Entropy in a closed system tends to a maximum


13.  Fundamental entropy equation 1


14.  Fundamental entropy equation 2


15.  Entropy and state space


16.  The Carnot theorem and the second law


17.  Carnot cycle efficiency


18.  A note on sign conventions


19.  Proof that V2/V1=V3/V4 for the Carnot cycle


20.  Why can’t we have a 100%-efficient engine?


21.  When an engine runs between T1 and T2, ht from T2 to T1 is impossible


22.  A thermodynamic definition for when T1>T2


23.  A temperature scale based on heat engine behaviour only


24.  Thermodynamic Kelvin temperature = Ideal gas Kelvin temperature


25.  The Clausius inequality


26.  A new property of state: entropy


27.  Equation for entropy change


28.  What the entropy change equation means


29.  How are these 2nd Law equations related to each other?


30.  Definition of a reversible process


31.  The TdS property relation is always true


32.  Reversible cycles have different efficiencies


33.  Irreversibility


34.  Calculating entropy change for a system with finite T difference


35.  ‘Lost’ work


36.  Why does dS=dQ/T (rev) ? -a special case

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