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Chemistry Report-PV=NRT
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Posted by: kbud---------------------
Every quarter I have to do a project relating to chemistry. Every one I did was about dirt bikes in some way. My latest i am proudest of. I used PV=NRT(you know, that equation that you,well-me, never thought would every be useful?). I showed the tire pressure increase when the temperature rises. I found it very interesting. About every 6 degrees, the pressure rises 1 psi.
Posted by: yzguy15---------------------
So if I show up to the track at 8:00 am and it is 88 degrees outside my tire pressure is x amount. By 8:45 (hey, I'm in Texas) when it's 94 degrees my tire pressure is x+1? Did you account for the values in the ideal gas law (PV=nRT) are atmospheres for pressure and degrees Kelvin for temperature. Not trying to nitpick, I really am curious. Sounds interesting!
Posted by: kbud---------------------
Yeah, there are holes in my project. Its not exact. I estimated on the volume of a tire so that could change things a little.
Posted by: Highbeam---------------------
Not if the volume stays constant, same thing happens in a blimp. To keep volume more constant, the tire should be on a bench.
Put all of your values into base units, Kelvin, absolute pressures, and assume you fill your tires with nitrogen as some folks do. Then it should work. I suspect you are pretty close despite these changes.
I love pivnert. We go way back. This law will chase you through physics too.
Posted by: firecracker22---------------------
For us who are not conversant with chemistry, physics and math, what is PV=NRT?
Posted by: kbud---------------------
Pressure X Volume = N (the number of moles of gas) X 8.31 (a general number) X temperature. I had to change my units or it wouldnt work
Posted by: VintageDirt---------------------
Don't forget that air is a combination of gasses and the partial pressure of each must be accounted for.
Here are some interesting Ideal Gas Law links from Google:
http://www-tech.mit.edu/Chemicool/idealgas.html
http://jersey.uoregon.edu/vlab/Piston/
http://intro.chem.okstate.edu/1314F...oratory/GLP.htm
http://dbhs.wvusd.k12.ca.us/GasLaw/Gas-Ideal.html
http://www.phy.ntnu.edu.tw/java/idealGas/idealGas.html
Why bother with all the mumbo jumbo when it's an accepted rule of thumb that for every 10°F change in air temperature inflation pressure will change by about 1psi:
http://www.tirerack.com/tires/tiret...al/pressure.htm
http://www.high-tec-retreading.com/tips.html
http://www.gmgoodwrench.com/TipsAdv...rePressure.html
:confused:
Posted by: Highbeam---------------------
Why bother?... because there are times when you must predict what should happen and then experiment to prove it. You may be in a situation where there isn't a rule of thumb or empirical data and you have to predict. As you let propane out of the bottle it gets cold. When you compress air in your compreesor or your diesel engine it gets hot. There are more moles of oxygen in cold air than in hot air, so you need more fuel!
The guy that built the first bridge had to be able to show that it would work before he built it and tested it out.
True, a normal guy will probably never actually plug numbers in to the equation after school but knowing the realtionship between P,V,n,and T will go a long way in theoretical planning.
I think the 8.31 is Boltzman's constant. That guy experimented with the variables in pivnert until he pulled the number out.
Posted by: VintageDirt---------------------
Quote:
Originally posted by Highbeam
The guy that built the first bridge had to be able to show that it would work before he built it and tested it out.
|
You may be right about everything but the bridge. 
Posted by: yzguy15---------------------
R= .0821 I believe. It's the ideal gas constant.
FC, the ideal gas law, more commonly referred to as pv=nrt is an equation to show the relationship of the pressure, volume, amount (moles), and temperature in an ideal gas. Can't remember what exactly makes the gas ideal, something about being constant I believe. Usually what it's used for is to find any one of those values when the others are at a constant.
R will always be the same number, .0821. Pressure is measured in atmospheres, volume in liters, n in moles (which is essentially the number of particles per atom, but that's a whole different topc in itself), and temperature in degrees Kelvin (which is degrees Celcius +273).
So say for a certain mixture of gases you have 2 liters of CO2 gas, in a container heated to 298 degrees Kelvin, with a atmospheric pressure 3 atm inside the container. Using your new formula you could plug the above numbers into the appropriate slot and, using simple algebra, find the number of moles in the sample of CO2 gas.
PV=nRT
(3 atm)*(2 L)=(x #of moles)*(.0821)*(298)
n = .204 mol CO2 gas
Now, why you would ever need to know this in a real life situation, I do not know. Hopefully this helps
Posted by: kbud---------------------
Thanks for the links vintage. I personaly probibly wont have to deal with this equation. I know a guy who works building pipe lines who has to deal with the ideal gas law every day. Gets paid a boatload too.
Posted by: OldassKDX---------------------
yz.....tsk tsk tsk. R is .08206 when its (atmospheres X Liters)/(mol X degrees Kelvin) but often we use R as 8.314 when its Joules/(mol X degrees Kelvin).....I mean c'mon, people might talk
PS,
if you're taking me seriously, you are right about using .0821 for PV=nRT
Posted by: Highbeam---------------------
Sorry VD, the bridge thing wasn't thought out all the way. I should have said when a guy builds a new style highway bridge, like say a cablestay bridge, he has to design it using formulas. Heck, when I design a sewer pipe I have to calculate the slopes, "downhill" won't work.
When you called my error, I was picturing a log laying across a canyon and some caveman walking across it.
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