Click here to go to the NEW College Discussion Forum

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.