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-   -   And for my next trick...more ideal gases questions. the joy. (http://www.physicsforums.com/showthread.php?t=109727)

QueenFisher Feb7-06 12:58 PM

and for my next trick...more ideal gases questions. the joy.
 
as promised:

a cylinder of volume 2x10^-3 m^3 contains a gas at a pressure of 1.50MNm^-2 and at a temperature of 300K.

calculate number of moles. i think i'm ok with this bit:
n=(pV)/(RT)
=(1.5x10^6)x(2x10^-3) all divided by 8.31x300
gives 1.2033694...

calculate number of molecules.
number of molecules=number of moles x avocado's constant
=1.2033694 x 6.023x10^23
=7.224283x10^23

calculate the actual mass of the gas if the molar mass is 0.032kg
actual mass = number of moles x molecular mass
=32 x 1.2033694
=38.5078

now calculate the mass of one molecule of the gas.
erk! which equation do i use? i can't use the half-m-c-squared-bar ones cos i don't know speeds or anything!
help is appreciated.

i have yet another one! watch this space.

Galileo Feb7-06 01:16 PM

Watch your significant figures. Really.
Also, use the units. The mass is not 38, but 38 kg.

So, you know the mass of the entire gas and you know how many molecules there are in the gas, but you cannot calculate the mass per molecule?

QueenFisher Feb7-06 01:25 PM

no the mass is 38 grams cos i converted the 0.032kg to grams when i put it in the equation.

but anyway i think that has solved my problem thanks!


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