CHEMISTRY QUESTION





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Discus: What Are My Chances?: January 2003 Archive: CHEMISTRY QUESTION
By Chem Loser on Sunday, January 12, 2003 - 09:49 pm: Edit

Question: Why is it necessary to use Kelvin rather than Celsius temperature in gas law problems?

By mo on Sunday, January 12, 2003 - 09:51 pm: Edit

because K never reaches zero and is always positive and covers a much larger temperature than Celsius. Also, the lowest K is the lowest temperature of any substance known as the absolute zero.

By quarky on Sunday, January 12, 2003 - 09:56 pm: Edit

mo, I am sorry, but you are totally wrong. First of all, your answer does not EXPLAIN why it is necessary to use K rather than degrees Celsius. Here's the real answer:

Chem Looza:
The problem is that the universally accepted gas law constant (R in the PV=nRT equation) has Kelvin as its units. If it were in Celsius, then you could use deg. C, but it's in Kelvin, so we have to stick with that :) BTW, there are two different "popular" R's -- they use different pressure units: Pascals and atm's. You could probably create a thrid one by using mm Hg or something :)

By jil on Sunday, January 12, 2003 - 10:11 pm: Edit

wow you're such a moron. the REASON we use K in the gas equation is for the reason mo mentioned. the fact that K is never negative and covers a wider range of temperatures and has an absolute zero. BTW, i got a 800 on SAT II Chem and a 5 on AP Chem

By cornell engineering, class of 2007 on Sunday, January 12, 2003 - 10:32 pm: Edit

The Kelvin temperature scale lets us create a completely linear relationship between temperature and volume, and a completely inverse relationship between temperature and pressure. You can't do this with fahrenheit and celsius, because they both go below zero, and volume and pressure can't be negative, obviously. But I am more of a physics (specifically mechanics) person, so someone whose a chemistry buff, correct me if I'm wrong.

By chemwhiz on Sunday, January 12, 2003 - 11:24 pm: Edit

The reason Kelvin was created at all is for the reasons Mo stated- but the reason it is the de facto unit in gas laws is because using C would completely throw you off, since R is in liter*atm/mole*kelvin.

By Chem loser on Sunday, January 12, 2003 - 11:33 pm: Edit

thanks!

By Pat57575 (Pat57575) on Sunday, January 12, 2003 - 11:45 pm: Edit

cornell engineering explained it perfectly.

By Pat57575 (Pat57575) on Monday, January 13, 2003 - 12:16 am: Edit

...except the relationship between pressure and temperature is also linear (not inverse). P and V are inversely related.

By vp on Tuesday, January 14, 2003 - 11:58 am: Edit

cornell enigneering is abs. correct

Basically in easier words:

We do problems where we say temperature is propotional to volume right? now how the hell are u gonna do that if ur temperature is split up in negative and postive values? Hence we use a nice little kelivin where the relation is completely linear AND the scale starts at zero. Therefore kelvin can be used in calculations/problems as well. Actually even celcius gives u a linear relation, but its split up between the first and fourth quadrants, and basically it makes a mess of things.

By ... on Tuesday, January 14, 2003 - 03:47 pm: Edit

also i believe that the units for R include a K somewhere in there. Therefore, in order for them to cancel out, (which is needed) u must use Kelvins.


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