Postulates of the kinetic theory

[h2579154]

regarding the postulates of the kinetic theory, in each book or page that are different, that is, in more and less sites... even in some cases with contradictory redactions, and hence my doubt... in one place I read a postulate: - There are no intermolecular forces except during the collision between molecules and yet in another place this appears as a postulate: Collisions between two molecules do not exert unattractive or repulsive forces... this is not contradictory...? are there or are there not intramolecular forces during the collision, according to the postulates of kinetic theory.????

[swansont]

26 minutes ago, h2579154 said:

in one place I read a postulate: - There are no intermolecular forces except during the collision between molecules and yet in another place this appears as a postulate: Collisions between two molecules do not exert unattractive or repulsive forces... this is not contradictory...? are there or are there not intramolecular forces during the collision, according to the postulates of kinetic theory.????

They are saying the same thing: the only force is that of the collision.

[studiot]

1 hour ago, h2579154 said:

regarding the postulates of the kinetic theory, in each book or page that are different, that is, in more and less sites... even in some cases with contradictory redactions, and hence my doubt... in one place I read a postulate: - There are no intermolecular forces except during the collision between molecules and yet in another place this appears as a postulate: Collisions between two molecules do not exert unattractive or repulsive forces... this is not contradictory...? are there or are there not intramolecular forces during the collision, according to the postulates of kinetic theory.????

Since you haven't told us any of your sources, and I can't imagine why the CIA would be redacting sections of text on the subject, I am going to have to guess as to what you are on about.

 

Assuming this is not a windup surely you know that many theories have a simple version and a more exact one?

The 'kinetic theory' is no different, in fact there are a whole graded series of versions introducing more and more effects as they become closer to reality.

 

So the simplest version assumes that the particles

1) Occupy zero volume or negilgable volume in relation to theri container volume.

2 Are only subject to forces of elastic collisions, both between the particles themselves and the particles and their container.

 

These assumptions lead to the ideal gas laws.

However neither are true in much of common experience so the gas laws are modified to take the actual volume of the particles into account and also again modified to account for interactions between particles.

Van Der Waal's equation is one such.

 

http://hyperphysics.phy-astr.gsu.edu/hbase/Kinetic/waal.html

Edited May 20, 2018 by studiot

[Guillem_dlc]

3 hours ago, swansont said:

They are saying the same thing: the only force is that of the collision.

Can I ask you a question?

So, the forces of the collision, which if they exist, are not of attraction or repulsion, are they??

[michel123456]

1 hour ago, Guillem_dlc said:

Can I ask you a question?

That is already a question.

[studiot]

2 hours ago, Guillem_dlc said:

Can I ask you a question?

So, the forces of the collision, which if they exist, are not of attraction or repulsion, are they??

 

The forces of collision are never of attraction or repulsion.

What made you think they ever could be?

[swansont]

6 hours ago, Guillem_dlc said:

Can I ask you a question?

So, the forces of the collision, which if they exist, are not of attraction or repulsion, are they??

Not in this context, of electrostatic and magnetic interactions, which depend on 1/r^n, where n is 2 or greater

It's modeled as hard-sphere elastic scattering. 

[Guillem_dlc]

14 hours ago, studiot said:

 

The forces of collision are never of attraction or repulsion.

What made you think they ever could be?

I searched on the Internet and found that there are no intermolecular forces except during the crash.

Then, I assumed that he meant that in the collision by the proximity of the molecules the forces of attraction of Van der Waals were at work again... I now see that no... I can say that there are intermolecular forces of collision but I can still say that there are no forces of molecular attraction... correct no??

[swansont]

1 hour ago, Guillem_dlc said:

I searched on the Internet and found that there are no intermolecular forces except during the crash.

Then, I assumed that he meant that in the collision by the proximity of the molecules the forces of attraction of Van der Waals were at work again... I now see that no...

In basic kinetic theory (ideal gases) there is no Van der Waals attraction. Though there is a model that uses it.

1 hour ago, Guillem_dlc said:

I can say that there are intermolecular forces of collision but I can still say that there are no forces of molecular attraction... correct no??

Correct.

[studiot]

 

1 hour ago, swansont said:

Quote

Guillem_dlc

I can say that there are intermolecular forces of collision but I can still say that there are no forces of molecular attraction... correct no??

Correct.

Guillem,

Not sure why you are making such heavy weather of it.

I said

17 hours ago, studiot said:

The forces of collision are never of attraction or repulsion.

What made you think they ever could be?

'Never' surely indicates that there must be separate and distinct forces that only occur during a collision.

Not before, not after, during.

That is during the short period of time that the colliding objects are in physical contact.

Because these forces only occur for short periods of time and are not constant during that time we do not normally work in terms of forces, but use the mechanics of momentum.

 

 

 

On the other hand forces of attraction/repulsion act continuously over time (but vary over space as swansont has indicated) and act whether or not the objects are in physical contact.

These forces have to be taken into account in the kinetic theory of ionic movement.

There are potentially yet more complicated forces available.

 

It is a matter of taste whether you consider the Kinetic Theory to cover only the simplest situation or extend it to Van der Waals, ions in solution, plasmas etc.
 

 

Edited May 21, 2018 by studiot