Physical Chemistry Discussion - Key Concepts & Equations

[jegues]

Hello all,

I've just started a class in physical chemistry and it seems to be progressing fairly slowly so I thought I'd start a thread so we could discuss some key concepts that are frequent in physical chemistry.

Keep in mind I haven't taken any courses in thermal dynamics yet so I am still a little sketchy in that topic of discussion.

Any key concepts/equations we can discuss?

I'm just looking to further my understanding with the little spare time I've got before I'm swamped with schoolwork.

Look forward to hearing from you!

 

[ChmDudeCB]

Physical Chemistry is the combination of quantum mechanics and thermodynamics via statistical mechanics.

Basically, if you finish the class you will be able to find information with quantum mechanics and use stat mech to determine thermodynamic information and vice versa.

Every professor is different. My professor taught us the mathematics of stat mech first, then thermo, and we are in the middle of quantum right now.

Post up some of the subject material you are covering and any derivations you have problems with. Most likely you're not too far off from stuff like deriving the ideal gas equation from Newton's equations. Also, post up the name an ISBN of your textbook.

I'm using Physical Chemistry, A Molecular Approach by Donald A. McQuarrie (UC) and John D. Simon (Duke) ISBN: 978-0-935702-99-6.

I like it, but I sometimes get lost in the derivations (my own fault most of the time) and the explanations are dry, even though the concepts are astounding.

OCW.MIT.EDU is also a godsend as you can never get enough lecture time. I learned thermo from the MIT lectures on youtube.

 

[cronxeh]

https://www.youtube.com/watch?v=kLqduWF6GXE

*GASP*

My heart just fibrillated when he said 'these laws are not proven.. '

Thx for thie video, haven't been to MIT website in a while, its a really great one

 

[ChmDudeCB]

haha no problem. I read an article in my university's paper debating whether or not we should do the same so I checked it out and found a whole new way to study...go to class two or three times a day!:!)


In other news we're starting operators, for instance [p,x] px-px = ih

h = h/2pi

 

[jegues]

Thanks for the vid, I don't have the time to watch it just this second but I'll certainly watch it later.

As far as our textbook, we're using "Chemistry: A Molecular Approach by Nivaldo J. Tro, ISBN: 978-0-13-100065-0".

We seem to progressing fairly slowly. We've only defined internal energy, enthalpy and last class we started heat of formation. It's all pretty straight forward for now.

 

[bonzoboy]

Ask about droplet formation in condensation vapor trails. Theory says that the vapor pressure of water is infinite for infinitely small diameters. So when you look at a vapor trail in the sky, my MIT professor friend says "it's because of small particles of material in the engine, abraded away, that act as condensation nuclei for the vapor to form".

Sounds good, maybe. But today I go outside, and there's not a vapor trail in the sky (yet there are aircraft all over, including refugee flights from Haiti). But no vapor trails. So what happened to the vapor trails (we did have a cold front blow through, but most trails I see are at fairly high altitude). So are the engines used in today's aircraft NOT abrading away and therefore NOT producing cloud condensation nuclei (the water vapor source is the combustion of the fuel).

Turning the problem around a bit, a plane lands at an airport where the air is nearly saturated (high relative humidity). A swirl of vapor comes of the end of each wing. So, if theory says that the vapor pressure is nearly infinitely for infinitely small droplets, then how did this trail form? What was the source of the nuclei? Was it dirt on the wings (the trail is not from the engine).

Hey if you get an answer...I'd love to hear it!

 

[Borek]

I always thought it is a soot in exhaust gases that provides nucleation sites.

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[bonzoboy]

Soot would have been my guess too (or sulfates); but I've had numerous academics quote "the metal abrading from the engine".

I remember a chap at an OEM who took an engine that had been running for years to see if he could weigh the engine, comparing original ship weight with final weight. No such luck.

But I'd agree with you.

But my observation last week (no contrails anywhere) was a bit mystifying...where had all the contrails gone?

 

[Borek]

Contrails are not always visible, obviously it depends on the relative humidity and temperature of the air plane is moving in. I remember reading somewhere that during combat missions military planes select the height they fly so that they don't leave contrails and are harder to detect.

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