Molar Volume

[Primarygun]

Does the molar volume of a given quantity of gas depend on the type of gas?

[Sisyphus]

No, not while it's a gas.

[timo]

And not on the quantity, either

[insane_alien]

nope. ~22.4 litre/mol for any given gas at STP.

[Bluenoise]

And not on the quantity, either

 

yuck yuck

[Borek]

It depends on conditions. When the temperature is high enough and pressure is low enough that the gas can be treated as ideal, kind of gas doesn't matter. The closer you are to the gas condensation, the less ideal gas is and the discrepancies between ideal and real behavior are larger. Note that it doesn't necesarilly mean some exotic conditions - water at 110 deg C and 1 atm is a non-ideal gas, methanol need 65 deg C to boil and to become non-ideal gas and so on.

 

One of the assumptions in the ideal gas theory is that the molecules have zero volume. That's never true, however, when the molecule size is much smaller than the distance between molecules, this assumption is meet well enough. When the pressure and temperature conditions gets such that molecules get close to each other, their size can be no longer neglected. Ideal gas equation (PV=nRT) doesn't hold then (look for the Van der Waals equation).

 

Note that in most questions where you will be asked about gas volume/number of moles you will be expected to use ideal gas approximation.

 

Best,

Borek

--

General Chemistry Software

www.pH-meter.info

[Primarygun]

It depends on conditions. When the temperature is high enough and essure is low enough that the gas can be treated as ideal, kind of gas doesn't matter. The closer you are to the gas condensation, the less ideal gas is and the discrepancies between ideal and real behavior are larger. Note that it doesn't necesarilly mean some exotic conditions - water at 110 deg C and 1 atm is a non-ideal gas, methanol need 65 deg C to boil and to become non-ideal gas and so on.

 

One of the assumptions in the ideal gas theory is that the molecules have zero volume. That's never true, however, when the molecule size is much smaller than the distance between molecules, this assumption is meet well enough. When the pressure and temperature conditions gets such that molecules get close to each other, their size can be no longer neglected. Ideal gas equation (PV=nRT) doesn't hold then (look for the Van der Waals equation).

 

Note that in most questions where you will be asked about gas volume/number of moles you will be expected to use ideal gas approximation.

 

Best,

Borek[/Quote]

Sorry, I should have been telling what I knew and if I had, you don't need to write so much.

I know the formula, but I see that carbon dioxide and some other gases may have different molar volume at a STP.

But my book, said all gases occupy the same volume at any condition.

Which is true?

[Borek]

my book, said all gases occupy the same volume at any condition.

 

Such statement holds only for ideal gases.

 

Best,

Borek

--

General Chemistry Software

www.pH-meter.info

[woelen]

I also want to add to Borek's explanation, that some gases also are far from ideal, even at low pressure, due to chemical equilibria.

 

Most common example is 2NO2 <---> N2O4

 

This equilibrium strongly affects the properties of NO2/N2O4 gas and this gas is far from ideal at any concentration.

 

However, for the majority of the gasses, this is not the case and then at sufficiently low pressure (better: sufficiently low relative partial volume of the molecules) they behave like ideal gasses.