Chemistry Help!

[TSE]

Hey guys, we are studying pressures, temperatures, etc. right now... and on my homework tonight I have a certain question I don't know how to answer...

The gas in a closed container has a pressure of 3.00 multiplied by 102 kPa at 30°C (303 K). What will the pressure be if the temperature is lowered to -172°C?

How do I do this problem and what is the answer? Thanks ahead of time!

 

[mknawabi]

PV = nRT
(pressure)*(volume) = (#moles)(universal gas constant)(temperature in kelvin)

plug in for pressure. don't count volume since it is a constant anyway. convert -172 to kelvin... do your algebra

 

[dukebound85]

Hey guys, we are studying pressures, temperatures, etc. right now... and on my homework tonight I have a certain question I don't know how to answer...

The gas in a closed container has a pressure of 3.00 multiplied by 102 kPa at 30°C (303 K). What will the pressure be if the temperature is lowered to -172°C?

How do I do this problem and what is the answer? Thanks ahead of time!

make sure you are using the right units for pressure. depending on how you have the mol ratio

 

[SLC Flyfishing]

You need to specify what the 3 in your pressure means. I'm assuming 3 atm. but if I'm not sure then I can't really help.

Knowing what unit you'll indicate the pressure with is of utmost importance when picking a value for the ideal gas constant.

SLC

 

[CorvusCamenarum]

I haven't had chemistry since my undergraduate days, but wouldn't the combined gas law be more effective here?

P1V1/T1 = P2V2/T2
As volume is constant, strike it from the equation: P1/T1 = P2/T2
P1T2 = P2T1
P2 = P1T2/T1
P2 = (P1*101)/303

(I'm a tad confused on the original pressure as well)

?

 

[mknawabi]

I haven't had chemistry since my undergraduate days, but wouldn't the combined gas law be more effective here?

P1V1/T1 = P2V2/T2
As volume is constant, strike it from the equation: P1/T1 = P2/T2
P1T2 = P2T1
P2 = P1T2/T1
P2 = (P1*101)/303

(I'm a tad confused on the original pressure as well)

?

Actually, you are most definitely right.

 

[SLC Flyfishing]

I haven't had chemistry since my undergraduate days, but wouldn't the combined gas law be more effective here?

P1V1/T1 = P2V2/T2
As volume is constant, strike it from the equation: P1/T1 = P2/T2
P1T2 = P2T1
P2 = P1T2/T1
P2 = (P1*101)/303

(I'm a tad confused on the original pressure as well)

?

That would be more efficient I suppose!

It's probably bad that I only remember the combined gas law when these sorts of things come up. Not that it's not able to deliver the correct solution, but still.........

SLC

 

[eddietr]

(I'm a tad confused on the original pressure as well)

The original pressure is 3.00 times 102 kPa. In other words, 306 kPa.

 

[CorvusCamenarum]

The original pressure is 3.00 times 102 kPa. In other words, 306 kPa.

Assuming you're correct, solving for P2 gives us 102 kPa.

 

[eddietr]

Assuming you're correct, solving for P2 gives us 102 kPa.

Sounds about right to me. And the equation you posted will hopefully help the OP see how you got that.

Intuitively, if :

1. You hold n,R, and V constant (closed container)
2. PV=nRT
3. you reduce the T to about 1/3 of the original condition.

then the pressure must be about 1/3 of the original also.

 

[TSE]

Thanks guys, I will show the professor tomorrow. Thank you for your help!