Talk:Avogadro's law

Untitled

The law as stated in this article is much stronger than I learned it in chemistry class. As I learned it, all Avogadro's law states is that the volume is proportional to the number of moles of gas if pressure and temperature is constant. It doesn't say anything about the relationship between the number of moles and the pressure (which would be a combination of Avogadro's law and Boyle's law) or about the relationship between the number of moles and the pressure (which needs Charles' or Gay-Lussac's law). It certainly isn't equivalent to the ideal gas law as this article seems to claim.

Agreed. Fixed. Hopefully :-) Vsmith 15:40, 12 Mar 2005 (UTC)

Why moles per volume is the same for all gases

It is remarkable that the volume of a mole of gas molecules is independent of the type (and I guess mixture) of molecules themselves. As a reader, I would very much like this article to provide an insight into why this is the case.AnthonyJamesWood 11th July 2006

That's a good question - I'll try to explain it as best I can:

I think it's best answered by understanding that the law only applies to a pair of volumes for which both the temperature and pressure are fixed. One volume (say hydrogen) at the same pressure and temperature will fill the same volume as an equal molar amount of nitrogen. In this case the nitrogen is heavier than the hydrogen molecules, but because it must have the same temperature and pressure as the H₂, its constituent particles must move a little slower (E_k=mv²). With the same temperature and pressure, it can easily occupy the same container as the other gas because it exerts no more force on the container walls, due to its particles moving slower, despite being heavier. If the N₂ molecules had the same speed as H₂, it would impact with greater force on the container walls and require a larger volume.

And just to relate the concept back to the other parameter, the amount of gas in moles, if we were now to take half the nitrogen gas away, it would only exert half as much pressure on the container walls (i.e. half as many collisions), and the container would collapse inwards significantly. Richard001 23:27, 25 December 2006 (UTC)

Richard001, I think this information would be very well placed in the article. Could you add it? Or if not, do you mind if I use an approximation of your wording here for the article? I feel that if I write it myself I may miss some subtlety. PatxiG (talk) 03:36, 14 February 2011 (UTC)

I agree that the main thrust of the article should describe the intuition / insight into why the Avogadro's law holds. An example that I've just thought about is to imagine a mole of Oxygen in its O form and then snap your fingers and have it magically turn into half a mole of Oxygen in its O₂ form. Intuitively the pressure can't have changed. The pressure is a statistical measure of trillions of trillions of particles randomly hitting the sides of the box; just because the particles will always now hit "in pairs" doesn't really affect the statistics. We'd also expect the volume to remain constant; nothing has really changed in terms of the total energy of the gas. Avogadro's law would seem to suggest that the volume would halve because we now (magically) have half as many moles. The get-out clause is that the temperature has doubled. The meaning of temperature is the average energy of a single particle; in the case of O pairing up into O₂, every particle just got twice as heavy while travelling at the same speed and therefore the temperature has doubled. This means that PV stays the same and nRT stays the same but by n (number of moles) halving and T doubling. DavidBoden (talk) 09:51, 2 July 2017 (UTC)

funny?? Weh?? XD

So assume we have gas 1 and gas 2 at the same temperature and pressures so they occupy the same volume, and have "N" particles.

So it seems intermolecular distances are adjusted such that regardless of the molecuar size, they somehow make volume constant.

seems funny to me that nature is so precise?? I mean take balls A and balls B of different sizes and they have some sort of love/hate attraction repulsion. The net effect is that balls A and balls B work out in a manner which is equal? —The preceding unsigned comment was added by 220.227.207.194 (talk) 14:12, 9 May 2007 (UTC).

It is funny that nature is so precise here... However, an important point is: Avogadro's law and the other laws like Boyle's law are valid only if the attraction and repulsion forces and energies between the molecules are small compared to the kinetic energy of the molecules. The pressure against the walls of the gas container is hardly due to repulsive forces between the molecules but rather due to the kinetic energy of the molecules which bounce against the walls, causing a force against it. The volume that the molecules take up is hardly related to their size or shape or to the forces between them, it is a function of their kinetic energy: that they need a lot of space since they are rapidly moving. —Preceding unsigned comment added by 141.52.232.84 (talk) 09:26, 21 November 2007 (UTC)

Cleanup needed

Article needs urgent cleanup as high priority, unref'd. --mervyn (talk) 22:42, 30 January 2009 (UTC)

I think it is a well-written and concise article about a rudimentary law of chemistry. Maybe it could use a little more detail, yes, but it really is very basic for most scientists. Mutomana (talk) 20:43, 16 January 2011 (UTC)

Molar volume

My calculations say, that when you use pressure 100 kPa, the volume would be 22.709 dm3. You can calculate that easily. TH 10:51, 22 October 2012 (UTC) — Preceding unsigned comment added by 158.194.65.113 (talk)

How could Avagrado know in 1811, before the Kinetic Theory of Gasses

Kronig developed that model in 1856, long after Avagrado. So take that knowledge away, and what made Avagrado propose his idea? Was it just a wild guess? I have never seen that explained properly, and t should form the core of the History section. Tuntable (talk) 23:38, 17 March 2019 (UTC)

1811 or 1812?

The article says both 1811 and 1812. Which is correct? --Palnatoke (talk) 15:32, 11 May 2020 (UTC)