Thermodynamics - When to use internal energy (U) or enthalpy (H)

Thermodynamics - When to use internal energy (U) or enthalpy (H) Like and subscribe! And get the notes here:
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[@Akeeets]

It's been 5 years since I've taken thermo and this question popped in my head. Great explanation.

[@kaana8421]

I'm retaking this class after failing it last year, and you've been quite helpful with my preparations for retake

[@Azakadune]

Oh my god, I’m usually a very good student, but reading the textbook is so much to take in; it leaves so much unsaid when giving me the formulas, this is an excellent example of that; my textbook and professor said squat about this. Thank you/

[@kylecatman7738]

This is the most important video to watch, thanks Dr ????? whoever you are... it explains why you use enthalpy on closed systems, which i kept seeing done on some problems and i was like why????? This tells you why, very useful video!!

[@FerasBiyikli]

Dude this is an amazing video btw, people need to understand the beauty of these equations. The cool thing about this video that it is timeless too. Good job sir, thank you

[@sevgipnar5261]

I dont undertstand in 4:08 shouldnt it be the equation is Q-W=H2-H1 ı mean why work becomes positive?? We derived the equation from negative Wout

[@kylecatman7738]

Flow work, like Boundary work is included in enthalpy, just wanted to clarify why we use enthalpy for flow systems as well as closed systems at constant pressure (boundary work like in pistons or balloons).

[@nicolascaleroarteaga4461]

Thanks a lot for all the videos, you made this class soooo easy!

[@gooddeedsleadto7499]

Boundary work & work out should be the same thing? Boundary work (PV) eventually becomes the shaft work? Why is it being subtracted twice from Q to get change in internal energy?

[@s4ulyaniv35]

Hi, thank you very much for your video. I don't grasp why we add the boundary work, isn't it comprised in work out?

[@kensonmalupande2424]

Great explaination

[@natasyakhaidir9380]

I cant understand before this you said expansion is positive then why now expansion is negative and out?

[@ayham_banna1]

4:08 shouldnt it be the equation is Q-W=H2-H1

[@mysticvaulttv]

i love your lectures but i hate how u changed all the signs of work in and work out, makes it soo confusing

[@engineeringdeciphered]

I like to teach Q+W=deltaH and then everything “in” is positive and everything “out” is negative. But it’s perfectly fine if you want to use Q-W=deltaH, so then you would say work “out” is positive and work “in” is negative. But you would still keep Q and energy as “in” being positive and “out” being negative.

[@mysticvaulttv]

@@engineeringdeciphered ok thank you. You're lectures are helping so much. Thank you again 🙏

[@shankarpalamootil8688]

So just to make sure, we minus expansion from your main equation because it is Wb out?

[@sunmichoi6888]

Thank you so much!

[@sethwilliams3683]

How about turbine problems or any problems with a mass flow rate? They always seem to use enthalpy and I'm not sure why...

[@engineeringdeciphered]

Yes, any time you have a moving fluid, use H because that takes the energy to move it into account.

[@sethwilliams3683]

@@engineeringdeciphered thank you for your quick response!! This video helped tremendously.

[@aasiqkumar732]

​@@engineeringdeciphered what? Can u explain little more

[@dremr2038]

Expansion is work out. Everything is positive if it "in".

[@selinaydemir9453]

someone have should this!!!!! gracias mucho

[@fatsow3639]

Thank you!!!!

[@khaledshebani8111]

Thank you... A clear and simple explanation. Can we connect via email or WhatsApp?

[@mebawubeshet6729]

I DONOT UNDERSTAND WHY U DO NOT USE Q out or W in ur equation

[@absolutcloud]

For the third equation, How do i calculate Qin individually ?

[@solounomas0]

Maybe you could calculate Qin=mass*Cp*(T2-T1)

[@solounomas0]

where cp is the specific heat capacity

[@jorgelevario3478]

Hey what about isothermal process ????

[@engineeringdeciphered]

It depends: if it is a constant temp AND constant pressure then use the first box. If it is constant temp AND constant volume then use the second box. But it is probably constant temp and neither const pressure or volume so you would use the last box. (I’m talking about the three boxed in equations at the 6:00-7:00 mark in the video).

[@jorgelevario3478]

@@engineeringdeciphered love the fact reply!!!!

[@jorgelevario3478]

fast*

[@jorgelevario3478]

Thank you so much!!! basically Isothermal does not dictate the behavior or which one to use. From my understanding.

[@jorgelevario3478]

I have exam Teusday and I have spent all semester looking for this exact video on the world wide web THANK YOU AGAIN!!

[@MirasolLusterio-v2s]

jhh🎉