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### Topic: Chemistry on pV=nRT  (Read 8878 times)

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#### cloud.conscript

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##### Chemistry on pV=nRT
« on: October 09, 2005, 01:30:51 PM »
i dont suck or anything... im just stuck on those and i really cant figure em

6- a pressure of about 1,0 x 10^-13 Pa is near emptiness. What would be the number of molecules that 1L of gas would contain at that pressure and at 0 degrees celcius (273 kelvins)?

9- At what temperature (in degrees celcius) must we bring a gas that is initially at -50 degrees celsius (223 Kelvins), if we want to pinput it in a container thats 3 times bigger and that its pressure is 5 times lower?

10- The pressure created by the air in a tire is of 175 kPa for a day with a -5 degress celcius temperature. The manufacturer recomends a maximal pressure of 250 kPa. would the recomandation be respected if, on a summer day, the temperature would be of 40 degrees celcius (313 Kelvins)? Why? (we suppose that the volume does not change.)
« Last Edit: October 09, 2005, 01:31:20 PM by cloud.conscript »

#### Lt.Pliskin

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##### Re:Chemistry on pV=nRT
« Reply #1 on: October 09, 2005, 02:24:37 PM »
Have you attempted any of these problems? I'll give you a few hints:

6- All you have to do is plug the numbers into the Ideal gas equation (rearranged to solve for n, since n= the number of moles of the gas) n= PV/RT

9- The combined gas law(I think thats what its called): P1V1/T1 = P2V2/T2 sould help

#### cloud.conscript

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##### Re:Chemistry on pV=nRT
« Reply #2 on: October 09, 2005, 02:41:05 PM »
""9- The combined gas law(I think thats what its called): P1V1/T1 = P2V2/T2 sould help""

isnt the correct law  p1V1/n1T1 = p2V2/n2T2; also the number of moles is not mentionned, so it wouldnt work...

#### Lt.Pliskin

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##### Re:Chemistry on pV=nRT
« Reply #3 on: October 09, 2005, 02:49:12 PM »
Im quite sure the equation I supplied is correct.

#### cloud.conscript

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##### Re:Chemistry on pV=nRT
« Reply #4 on: October 09, 2005, 03:28:37 PM »
recheck it because it doesnt make sense:

pV=nRT
pV/t=nR and not pV/T=R

#### Lt.Pliskin

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##### Re:Chemistry on pV=nRT
« Reply #5 on: October 09, 2005, 03:44:03 PM »
The ideal gas equation is used to solve for a variable at the moment of recording. The combined gas law is used to solve foor a variable after another variable has been changed.

PV = nRT                : no change
P1V1/T1 = P2V2/T2  : change

these two are not related in the sense that you are proposing.

http://members.aol.com/profchm/comb_gas.html

#### Garneck

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##### Re:Chemistry on pV=nRT
« Reply #6 on: October 09, 2005, 04:15:45 PM »
isnt the correct law  p1V1/n1T1 = p2V2/n2T2; also the number of moles is not mentionned, so it wouldnt work...

You aren't correct, because if we're talking about the same gas, then the number of moles is a constant number

#### Donaldson Tan

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##### Re:Chemistry on pV=nRT
« Reply #7 on: October 16, 2005, 09:15:08 AM »
6- a pressure of about 1,0 x 10^-13 Pa is near emptiness. What would be the number of molecules that 1L of gas would contain at that pressure and at 0 degrees celcius (273 kelvins)?
PV = nRT => n [moles] = PV/RT where P = 1.0 x 10-13 Pa, V = 1L = 0.001m3, R = 8.314

9- At what temperature (in degrees celcius) must we bring a gas that is initially at -50 degrees celsius (223 Kelvins), if we want to pinput it in a container thats 3 times bigger and that its pressure is 5 times lower?
in both conditions, the number of moles of gas is the same. PV = nRT would therefore suggest PV/T = nR = constant for both conditions. So you can find T using P1V1/T1 = P2V2/T2. You are given T1 and P1 = 5P2, V2 = 3V1, you can cancel out the common terms on both sides of the equation P1V1/T1 = P2V2/T2

10- The pressure created by the air in a tire is of 175 kPa for a day with a -5 degress celcius temperature. The manufacturer recomends a maximal pressure of 250 kPa. would the recomandation be respected if, on a summer day, the temperature would be of 40 degrees celcius (313 Kelvins)? Why? (we suppose that the volume does not change.)
PV = nRT => P = nRT/V
given volume is fixed, pressure of the tyre is directly proportional to the absolute temperature of the tyre.
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