B Deriving pV=NkT from N=Na*n and k=R/Na

  • B
  • Thread starter Thread starter Hannah7h
  • Start date Start date
AI Thread Summary
The discussion centers on deriving the ideal gas law, specifically transitioning from pV=nRT to pV=NkT using the relationships N=Na*n and k=R/Na. Participants clarify that simply manipulating definitions of constants does not yield the ideal gas law, which is applicable only to ideal gases. A model of ideal gas behavior is necessary, focusing on the relationship between pressure, particle concentration, and average speed. Key assumptions for the derivation include the discreteness of gas molecules, their non-interaction, and elastic collisions with container walls. The conversation concludes with a reference to a video that aids in understanding the derivation process.
Hannah7h
Messages
39
Reaction score
0
I've attempted to use N=Na*n -where N is that total number of particles of a gas, Na is the Avogadro constant and n is moles. And then attempted to use k=R/Na -where k is the Boltzmann constant and R is the molar gas constant. I got as far as N/n=R/k but then not sure how to get from this to the final equation- if this is even the right way
 
Physics news on Phys.org
You cannot get the ideal gas law by just manipulating the definition of Avogadro number and its relationship with other constants.
Whereas the definition of Avogadro number's is very general, the ideal gas law is valid only for ideal gases. So you need to start with a model of ideal gas and find a relationship between pressure and other parameters.
For example,try to find how the pressure depends on the concentration of particles and their average speed.
You can find the this done in introductory books on kinetic-molecular theory of gases.
 
Hannah7h said:
I've attempted to use N=Na*n -where N is that total number of particles of a gas, Na is the Avogadro constant and n is moles. And then attempted to use k=R/Na -where k is the Boltzmann constant and R is the molar gas constant. I got as far as N/n=R/k but then not sure how to get from this to the final equation- if this is even the right way

Are you trying to convert pV=nRT to pV=NkT?

It would help you are clear on what you want to do, especially on your starting point.

Zz.
 
ZapperZ said:
Are you trying to convert pV=nRT to pV=NkT?

It would help you are clear on what you want to do, especially on your starting point.

Zz.

Ah yeah sorry, it wasn't clear, basically I wanted to know what you would derive pV=nRT from and then how you would derive it from those equations, but also it would be good if you could tell me how to get from pV=nRT to pV=NkT
 
The gas constant is just ##R=k_B N_a##.
 
I think I know what you are looking for.
First, you make a few assumptions :

  • The gas is made up of discrete molecules
  • These molecules don't interact with one another
  • The gas molecules collide elastically with the walls of the container
  • The gas molecules occupy no relevant Volume
  • The gas molecules move equally in all three dimensions
I am just going to stop here because I remembered a video on this:

The derivation starts at 9 minutes
 
Tazerfish said:
I think I know what you are looking for.
First, you make a few assumptions :

  • The gas is made up of discrete molecules
  • These molecules don't interact with one another
  • The gas molecules collide elastically with the walls of the container
  • The gas molecules occupy no relevant Volume
  • The gas molecules move equally in all three dimensions
I am just going to stop here because I remembered a video on this:

The derivation starts at 9 minutes


Ohhh ok, I see how its done now, thank you
 
Glad I could help

Tazerfish :biggrin:
 
  • Like
Likes Hannah7h
Back
Top