What is the chemical potential of a diatomic gas in equilibrium?

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Homework Help Overview

The discussion revolves around determining the chemical potential of a diatomic gas in equilibrium, specifically focusing on the potentials of individual atoms and diatomic molecules. Participants explore the relationships between these potentials and the relevant equations governing them.

Discussion Character

  • Conceptual clarification, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • The original poster attempts to find the chemical potential of atoms and molecules, questioning how to derive the potential for diatomic molecules using the partition function. Some participants express uncertainty about the correctness of the equations presented and the relationships between the chemical potentials.

Discussion Status

The discussion is active, with participants questioning the validity of certain equations and clarifying the stoichiometry of the reaction involved. There is a focus on understanding how the chemical potentials relate to each other, particularly through Gibbs' condition.

Contextual Notes

Participants are navigating through assumptions about the relationships between atomic and molecular chemical potentials, with some equations being contested. The context includes the need to adhere to specific thermodynamic principles while deriving these relationships.

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Homework Statement
Consider the formation of diatomic molecules $$A_2$$ out of atoms $$A$$. Assume that the binding energy of the molecule is $$I$$, i.e., the difference in internal energy between a molecule and a pair of atoms is $$−I$$. Show that in the limit when the atoms and molecules may be regarded as classical ideal gases, except for the formation of the molecules, the equilibrium densities of the atoms and molecules satisfy $$\frac{nA_2}{n_ A^2} = √ 8λ 3 Ae I kT $$.
Relevant Equations
$$\mu_{A_2}+\mu_{A}=0$$
It is my assumption that I need to find the chemical potential of the atoms $$\mu_A$$ and for the molecules $$\mu_{A_2}$$,
then use $$\mu_{A_2}+\mu_{A}=0$$ to arrive at the given identity. For $$\mu_A$$, I found that $$\mu_A=k_BTln(n_A\lambda ^3)$$, where
$$n_a=\frac{N_a}{V}$$ and $$\lambda$$ is the thermal wavelength. My question is, how would I go about find $$\mu_{A_2}$$? I know I can find it using the partition function. But I am unsure what that would be in this case. Any advice helps. Thanks
 
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8λ3AeIkT

I suspect some sub/superscripts were needed here?
 
I don't understand your question. You have an equation relating ##\mu_A## and ##\mu_{A_2}##.

Note however that that equation is incorrect.
 
Yes, the equation should actually read $$\frac{n_{A2}}{(n_A)^2}=√8λ^3e^{\frac{I}{kT}} $$. Apologies.
 
DrClaude said:
I don't understand your question. You have an equation relating ##\mu_A## and ##\mu_{A_2}##.

Note however that that equation is incorrect.
I'm essentially trying to use the Gibb's condition ($$dG=0$$) to find how the chemical potential of the diatomic molecules relates to that of the atoms.
 
Diracobama2181 said:
I'm essentially trying to use the Gibb's condition ($$dG=0$$) to find how the chemical potential of the diatomic molecules relates to that of the atoms.

What is the stoichiometry of the reaction?
 
DrClaude said:
What is the stoichiometry of the reaction?
Two atoms create one molecule. So would the relation be $$2\mu_{A}=\mu_{A_2}$$?
 
Diracobama2181 said:
Two atoms create one molecule. So would the relation be $$2\mu_{A}=\mu_{A_2}$$?
Yes.
 

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