Need help on a Chem Question...

EternityOfPain · Post by **EternityOfPain** » Mon Oct 16, 2006 2:36 pm

Question: A sample of hydrogen gas, collected at 100 C and 1.0 atm., has a volume of 350 ml (0.350 lit.). What will be the pressure after it is transferred to a 4.0 lit. flask and cooled to 25 C? (temp must be in degrees of Kelvin)

I had assumed using the formula V2 = P1 X V1 / P2 but i am not getting anything that makes sense. I think its two formulas needed but am not sure. Any assistance would be greatly apperciated.

Cloud · Post by **Cloud** » Mon Oct 16, 2006 2:38 pm

I cannot predict the future.

RoboFlonne · Post by **RoboFlonne** » Mon Oct 16, 2006 5:10 pm

I haven't done any of these in around 4 years...

I think you need to use the Ideal Gas law.

PV=nRT

R=0.0821 liter - atmospheres per mol - degree

RoboFlonne · Post by **RoboFlonne** » Mon Oct 16, 2006 5:13 pm

I'm almost certain you need to use Kelvins instead of Celsius in that equation.

Cloud · Post by **Cloud** » Mon Oct 16, 2006 5:13 pm

You sound convincing. And then what would I do?

RoboFlonne · Post by **RoboFlonne** » Mon Oct 16, 2006 5:18 pm

Well cloud after using both equations to get your answer.

I would sneak into Chem lab and borrow a liter of Hydrogen in a flask to test and see if your answer is correct.

If your answer is wrong then go ahead and light the Flask because that's how all great scientists start out. After blowing many things up...

:dbz:

rallihir · Post by **rallihir** » Mon Oct 16, 2006 5:44 pm

Did you come up with 0.07 atms? The ideal gas law will allow you to calculate the number of moles of H2 at 100 degrees C (370 degrees K) [T1]. This should equal 0.0115 moles. Plugging that (n) back into the ideal gas equation with a change in the volume (V2) and change in the temperature (T2) should give you 0.07 atms.

(1.0atm)x(0.35L) = n(0.0821)(370 K) (P1)(V1)=nR(T1)
n = 0.0115 moles

(P2) = nR(T2)/(V2)

I think the problem with your initial pressure/volume ratio is that it does not take into account the change in pressure due to decreased temperature.

Hope that helps.

EternityOfPain · Post by **EternityOfPain** » Sat Oct 21, 2006 2:04 pm

^

Thanks for all the help guys, yea I found out that the answer was 0.70 ATM.

Cloud · Post by **Cloud** » Sat Oct 21, 2006 2:05 pm

When was this exactly?