Professor Steven stuart thank you for this beautiful professional unique presentation and I appreciate you for answering ppl questions and replying their questions. You're such a great person and incredible scientist ❤.
Professor I have a question here. Is Carnot cycle totally isothermal? I mean there are two isothermal processes, which are isothermal compression and isothermal expansion. Others are adiabatic compression and adiabatic expansion. These adiabatics are also isothermal, at the same time ?
No, definitely not. The adiabatic steps are not isothermal. The temperature decreases during an adiabatic expansion, and increases during an adiabatic compression. Notice also that the adiabatic steps on the PV graph move the system from one temperature (one isotherm) to another.
sir simple isothermal process also converts heat into work so what benefit do we get by such multistep process if instead, we can just expand or compress a gas isothermally because in the end the carnot cycle is also equivalent to an isothermal process
Yes, you're right, an isothermal expansion also converts heat into work. But to make an engine, with repeated cycles of heat -> work conversion, you have to get back to your starting point. If you just isothermally compress back to your starting point, it costs you (at least) as much work to compress as you gained from the expansion. The purpose of the adiabatic steps in the Carnot cycle are to get to a lower temperature so that the isothermal compression won't require as much work, and then to heat back up to the starting point. There are certainly other choices other than adiabatic expansion that could be used instead. The Carnot cycle is just the name we give to the cycle that uses isothermal + adiabatic volume changes. A Stirling cycle uses isochoric (constant-volume) steps to do the heating/cooling. Engineers learn about Otto, and Brayton, and Diesel, and other types of engine cycles. But physical chemists usually just care about the general concept of a heat engine, and Carnot is just the specific type that usually gets taught. The Carnot cycle was important, historically, because it allowed some thermodynamic proofs of the efficiency of heat engines. That's probably the main reason it is still taught as the first example of a heat engine. It's also helpful at this point in the course to review / reinforce the features of adiabatic volume changes.
The internal energy of an ideal gas depends only on its temperature, not on its volume. So the internal energy change is ΔU = n C_V ΔT, even when the volume is changing.
Yes, this constant-V subscript often causes unnecessary confusion (including for me, momentarily, in this video, as you noticed). For this ideal gas, U is proportional to T. Perhaps U = 3/2 nRT or U = 5/2 nRT or whatever. Generally speaking, U = n C_V T. Note that there is no volume dependence in this equation. So it turns out that, even when the volume is not constant, ΔU = n C_V ΔT.
@@rashakhaleel4337 I see. You mean the internal pressure, Π_T. I don't use that term, so I didn't recognize it right away, sorry. The internal pressure is (∂U/∂V)_T. I derive a thermodynamic equation for this derivative as an example in the video on the change of constraint rule: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-wFI1ZktuQeM.html . But I don't have a video that goes into any depth on the meaning or significance of the internal pressure for non-ideal gases.
