Adiabatic Processes

[@blastunlimited]

I really thank you sir all the way from an other continent about this incredible videos . just one question ,isn't dQ=ncdT? because you have said at 5:30 that du=ncdT which is true only if we have isochore process. please correct me if I am wrong .

[@jeffmachnvielscheisn6997]

this is right, if we don’t have an adiabatic system

[@IceHockeyCreamer]

How can P=nRT/V and P=const/(V)^gamma. Surely they give you two different functions?

[@PhysicalChemistry]

As you mentioned in your later comment, both are true (if the gas is ideal). In fact, substituting the ideal gas law into the P-V adiabatic expansion equation can give you a V-T or P-T relationship for adiabatic expansions

[@Jaylen-nq4vd]

Hi, why del U = CvT but not CpT

[@gavdownes100]

because it is in relation to volume not pressure

[@IceHockeyCreamer]

Apologies for previous comment. I forgot T also varies with V lol

[@PhysicalChemistry]

No worries. Glad you figured it out on your own

[@salaphysics6558]

Like all other people who try to impse a mathematical solution onto a physics action, you also give absolutely NO information about the actual process that nature uses to do this adiabatic cooling and heating thing. There is an underlying process going on but, I can assure you wont like it and that you;'ll most likely have no interest in it. But, I will give a hint: Since temperature is related to the speed of particles (the relationship between the speed of sound and temperature being a good and convenient example) and since the adiabatic process makes things warmer and cooler, it must somehow be changing the speed of the particles. Or you may disagree with that and say that it doesn't. If I'm right and it does, then the act of both compressing the...particles...and of expanding them (or at least creating the conditions for them to expand themselves) and that it results in the particles moving faster or slower, there's a step missing in the mathematical modeling; ie: HOW the particles are moving slower or faster. I've seen the usual nonsense of the speed of the piston (which you use in your example) as being something that adds its speed to the particles during compression. But, that doesn't explain why there's no correlation between the speed of the piston and the change in temperature or how withdrawing the piston cools the particles using the same lame rationale. I'll give one additional hint. The missing piece is something salaphysics refers to as a "lock". When particles collide and exchange their energy, momentum, oomph (or whatever you choose to call what particles in motion have to determine their temperature) the closing speed of the particles drops to zero (and lock) and at that time both particles in the collision are moving more slowly than they were. After some time, the lock somehow (which needs to be figured out) spontaneously breaks and the particles then use the energy in the lock to fly apart again. If you're a scientist, that should be enough information to at least get your brain working as to what happens during the lock that relates to the adiabatic processes observed. See. I didn't lie. I told you that you wouldn't like it. However I did lie when I said I'd give a hint and then gave two hints (so sue me). salaphysics.com 060323

[@PhysicalChemistry]

Adiabatic heating / cooling is a thermodynamic process, not a kinetic one. So any explanation that uses the speed of the piston to explain heating or cooling is incorrect. The temperature change comes from the energy spent in doing PV work, i.e. an exchange between kinetic and potential energy.

[@salaphysics6558]

@@PhysicalChemistry - a different video came up for this notice in my mail box. Sorry about that but, the data is good. I have NO idea what's happening with these comments. My last rather lengthy comment is gone and at this point I can't be sure who I'm even responding to. Did you delete my earlier comment I posted today????

[@PhysicalChemistry]

@@salaphysics6558 No, I haven't deleted any comments

[@salaphysics6558]

@@PhysicalChemistry - I found the other video but, not my comment. If it's okay with you I'll repost the comment (with edits to tailor it to YOUR video). I question your comment that, "The temperature change comes from the energy spent in doing PV work, i.e. an exchange between kinetic and potential energy".

[@PhysicalChemistry]

@@salaphysics6558 You don't need my permission to post. The discussion under all of my videos is open