01. Thermodynamics: Carnot engine, Entropy, Helmholtz/Gibbs free energy

0:00 Introduction
1:50 The steam engine
3:44 Carnot's most efficient engine
7:05 Reversible and irreversible processes
9:01 The Carnot cycle
10:56 The ideal gas law
12:27 Mathematical analysis of the Carnot cycle
18:15 Adiabatic processes
22:43 Efficiency of the Carnot engine
24:29 Entropy
27:50 Spontaneous processes
29:50 Helmholtz free energy
31:24 Gibbs free energy
33:23 Summary

[andymason]

Oh my god. I cannot even begin to explain how elegant this video is. It’s a hidden goldmine of explanations that actually raise the understanding of thermodynamics on a fundamental level. Bravo.

[jackdaniel]

the best thermodynamic explanation ever made thumb up

[declanwk]

I have always struggled with this topic, thank you for this very clear exposition. One thing that used to confuse me, was I thought that in the Carnot engine, gas had to flow from the hot to the cold reservoir. But from your video (and from considering a toy Stirling engine) it is clear that only heat needs to flow from the hot reservoir into the piston and then from the piston into the cold reservoir (with some of the heat energy converted into work). In many heat engines gas does flow from the hot to the cold reservoir but it is not necessary to consider for this analysis. The same amount of gas can remain in the piston throughout the cycle.

[valentinussofa]

Great lecture series. I subscribed this channel. Thank you very much Sir. From Indonesia🇮🇩🙏

[bansikhunt]

Love this series, thanks a lot for your affort, time & energy putting in this masterpiece!

[diyaazaghloul]

Amazing video thank you for sharing this information

[nosms]

Hello sir. This serie is the best explanation of thermodynamics I have ever watched.
I also watched your serie about optics which was very helpfull.
I wonder if you made a lecture note on thermodynamics as you did for optics. Because the lecture note on optics was amazing. Thank you sir

[joeboxter]

@27:28 the simplified form of clausis inequality may have an error. You have used Th and Tc and so that is the same as the original equation where you got a positive result. However, you get a negative result the second time and say that you are not considering the Temperature of the reservoirs as before. But the equation says otherwise. You say you are considering the temperature of the surrounding. And indeed that is what you say in the integral equation.

I believe what you mean is Qin/Ts -+ Qout/Ts < 0, not what you have Qin/Th + Qout/Tc. Because the Work is 0. Qin/Ts is > 0. But Qout/Ts is < 0 and Qout < Qin which means it has to be negative. As oppose to the original Qin/Th + Qout/Tc is > 0 because Th > Tc and Qin and Qout are opposite. And by convention Qin is positive and Qout is negative. It's the denominator Tc > Th that makes the whole thing positive.

Excellent video, though. I don't think I've ever seen such a comprehensive treatment. You almost sound more like a chemist or mathematician and not a physicist. For whatever reason, I find physicists tend to be more sloppy with the book keeping than are chemists and mathematicians.

[intuitivelyrigorous]

I think at 18:41, you shoud write the extra ∆P∆V which would then approximate to 0 when taking ∆P and ∆V as dP and dV.

[StefanHoffmann]

9:30 Why is this process reversible, when at 7:53 it is said that moving a piston connected to a hot reservoir is an irreversible process. It probably has to do with the fact that the temperature is kept constant when expanding the gas, but I do not see why this leads to a reversible process? Also, keeping the temperature constant while compressing the gas when it is connected to a hot reservoir should not be possible at all, or what am I missing here?

[intuitivelyrigorous]

27:26 is little confusing to me. What i understand is first you defined entropy as [ heat given(+) or heat taken(-) to system] / T . Which always increases as you showed from 2nd law assumption. Then you said "in clausius inequality we are calculating entropy of engine not reservoir moreover we are dividing it by temperature of reservoir, hence it does not contradicts that entropy increases " In this statement their are lot of holes in my mind, the way you said it ... I feel like it means that in clausius inequality we are not measuring the entropy at all since dividing given heat to engine by temperature of reservoir is not how you defined entropy and hence it does not contradicts 2nd law. But another teacher actually defined entropy and derived 2nd law using clausius inequality infact what your 2nd law states is what actually he referred to as the clausius inequality. I know different teacher call things with different names. But the confusion from 27:26 remains in my mind and it's unclear what you actually meant. Thanks. Very insightful video.

[jacobvandijk]

@ 31:25 A "closed isolated" system??? An open system, but no flow of particles??? You always surprise me, Sander.