pressure when given temp and time

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pressure when given temp and time

Postby Nicolette_Canlian_2L » Tue Jan 08, 2019 11:27 pm

I'm not sure how to approach this problem. In the 7th edition, it is part of the self test 3B.2A.
A rigid oxygen tank stored outside a building has a pressure of 20.00atm at 6:00am, when the temp is 10 degrees celsius. What will be the pressure in the tank at 6:00pm, when the temp is 30. degrees celsius?
Do we need to set up a ratio?

Michelle Fu 1H
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Joined: Fri Sep 28, 2018 12:19 am

Re: pressure when given temp and time

Postby Michelle Fu 1H » Wed Jan 09, 2019 9:08 am

I'd assume you use PV = nRT. In the first part of the problem you are given the pressure, R and the temperature which are P, R, and T respectively. The key thing here is to solve for n, and we do that by moving everything to the left side of the equation: PV/RT = n
We know that the number of moles is constant (no moles of gas are lost in a sealed environment) so we can say PV/RT = P2V2/RT2 where P2V2/RT2 yields the number of moles when the tank is at 30 degrees celsius. Because volume is the same and unchanged we can divide both sides by V or V2, leaving us with

P/RT = P2/RT2

R is also a constant between the two so

P/T = P2/T2

Thus we can plug our known constants P and T given to us, as well as the final temperature T2 to get P2, or the final pressure.

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