System Pressure

[The Cancer Cure]

I'm sorry for this second question, but I am very lost in this chapter. I have no idea what to do on this problem. Please advise me.

 

gas pressures

 

N2 245 torr (1 L)

 

Ne 745 torr (1 L)

 

H2 489 torr (.5 L)

 

Each of the bulbs contains a gas at the pressure shown. What is the pressure of the system when all the stopcocks are opened, assuming that the temperature remains constant? (We can neglect the volume of the capillary tubing connecting the bulbs.)

 

Thanks guys.

[toastywombel]

Well when the stopcock is opened I would imagine that gas would escape and the pressure would be 0, assuming that the gas has somewhere to escape to and that its not sucked out. Then the pressure would be negative.

[hermanntrude]

yuck.

 

I've seen questions like this before with two bulbs but not three. nasty question. however, what you need is a modified version of boyle's law (notice the numbers of moles and the temperature is constant. that should always scream "boyle" to you).

 

basically the sum of the products of the pressures and volumes in the three separate flasks should equal the product of the pressure and volume of the single container after the stopcocks are opened:

 

[math](P_{1}V_{1})+(P_{2}V_{2})+(P_{3}V_{3}) = P_{final}V_{final}[/math]

 

where the subscipts 1,2 and 3 represent the values for the three flasks.

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Well when the stopcock is opened I would imagine that gas would escape and the pressure would be 0, assuming that the gas has somewhere to escape to and that its not sucked out. Then the pressure would be negative.

 

the stopcocks are between the flasks, i suspect. Also there's no such thing as a negative pressure. if the flasks were opened to the atmosphere, the final pressure would be atmospheric pressure.

[The Cancer Cure]

So it should be 245 + 745 + 244.5 = 1234.5 with three significant figures = 1240 torr?

 

I tried 1240 torr (I'm using WebAssign by the way) and it gave me feedback that the answer was incorrect.

 

What do you think is wrong?

[toastywombel]

yuck.

 

I've seen questions like this before with two bulbs but not three. nasty question. however, what you need is a modified version of boyle's law (notice the numbers of moles and the temperature is constant. that should always scream "boyle" to you).

 

basically the sum of the products of the pressures and volumes in the three separate flasks should equal the product of the pressure and volume of the single container after the stopcocks are opened:

 

[math](P_{1}V_{1})+(P_{2}V_{2})+(P_{3}V_{3}) = P_{final}V_{final}[/math]

 

where the subscipts 1,2 and 3 represent the values for the three flasks.

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Merged post follows:

Consecutive posts merged

 

 

the stopcocks are between the flasks, i suspect. Also there's no such thing as a negative pressure. if the flasks were opened to the atmosphere, the final pressure would be atmospheric pressure.

 

Yeah I really was taking a random guess, I had to look up what a stopcock was haha. And thats why you will find me in the physics section most of the time ! I hope you guys get this problem rocked though! Good Luck!

[hermanntrude]

So it should be 245 + 745 + 244.5 = 1234.5 with three significant figures = 1240 torr?

 

I tried 1240 torr (I'm using WebAssign by the way) and it gave me feedback that the answer was incorrect.

 

What do you think is wrong?

 

1234.5 is Pfinal x Vfinal. Divide by the volume of the final system

[The Cancer Cure]

Thank you so much!

 

I'd keep clicking reputation but it won't let me.

[hermanntrude]

lol no problem!

 

My students have their final exam tomorrow and I wish at least one of them cared half as much as you seem to.

[Phi for All]

I'd keep clicking reputation but it won't let me.

We don't give hermanntrude enough recognition for the great work he does here, so I'll give him some more for you.

[hermanntrude]

We don't give hermanntrude enough recognition for the great work he does here, so I'll give him some more for you.

 

thanks man!

[The Cancer Cure]

We don't give hermanntrude enough recognition for the great work he does here, so I'll give him some more for you.

 

Thank you. :-p