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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: felic2010 on February 23, 2010, 11:51:01 AM

Title: Gas Question
Post by: felic2010 on February 23, 2010, 11:51:01 AM
Hi. Just wondering if anyone can help me with how to answer the following question. Kind of confused as to what Im meant to do.

Q. A flask is filled with nitrogen gas at STP. If the total number of molecules in the flask is 2.25 x 10 22, what is the volume of the flask in cm 3?

Thanks
Title: Re: Gas Question
Post by: Borek on February 23, 2010, 12:06:58 PM
What STP means? What equations combining number of moles, volume and temperature do you know?
Title: Re: Gas Question
Post by: felic2010 on February 23, 2010, 12:16:44 PM
STP means Standard Temperature and Pressure.
Standard temperature is 273 K
Standard Pressure is 100 kPa

I know number of molecules = number of moles by Avogadros constant
So I can work out the number of moles to be Moles x 6 x 10^23 = 2.25 x 1022 and that gives an answer of 0.0375

But its here I get lost.

I know the equation pV = nRT but what could I use as R (the gas constant) here? is it 8.31?
100 x V = .0375 x 8.31 x 273

Is this on the right track? 0.85073
But then the answer asks for cm3 and Im noit sure what Im doing then.

Or do I need to somehow find values to fit into the equation

p1v1/t1 = p2v2/t2 ?
Title: Re: Gas Question
Post by: Schrödinger on February 23, 2010, 01:38:04 PM
Quote from: felic2010 on February 23, 2010, 12:16:44 PM
STP means Standard Temperature and Pressure.
Standard temperature is 273 K
Standard Pressure is 100 kPa

I know number of molecules = number of moles by Avogadros constant
So I can work out the number of moles to be Moles x 6 x 10^23 = 2.25 x 1022 and that gives an answer of 0.0375

But its here I get lost.

I know the equation pV = nRT but what could I use as R (the gas constant) here? is it 8.31?
100 x V = .0375 x 8.31 x 273

Is this on the right track? 0.85073
But then the answer asks for cm3 and Im noit sure what Im doing then.

Or do I need to somehow find values to fit into the equation

p1v1/t1 = p2v2/t2 ?


1 . Avogadro's number = 6.022 x 1023

2 . 100kPa = 100000 Pa

3 . http://en.wikipedia.org/wiki/Gas_constant. (Try converting Pa in terms of Joules and
     metres)

4 . Once you get the answer (which will be in m3 if you use R = 8.314 Jmol-1K-1), convert it into
    cm3.