Chemical potential (statistical physics)

In summary, the chemical potential for a photon or phonon gas is zero because the number of particles can fluctuate freely without changing the system's free energy. This means that the average number of particles is determined by the system's state. Additionally, in thermal equilibrium, the number of photons is not a thermodynamic variable, but rather its average can be calculated. This is because the chemical potential and number of particles are conjugate variables in equilibrium thermodynamics.
  • #1
Edgardo
706
17
Hi all,

I have a question about the chemical potential [itex]\mu[/itex] from statistical physics:
Why is the chemical potential [itex]\mu[/itex] for a photon gas (or phonon gas) zero?

Thanks in advance

Edgardo
 
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  • #2
That is because a number of both phonons and photons can fluctuate freely without changing the free energy of the system. So their average number is determined by the system state.
 
  • #3
The # of photons is not a thermodynamical variable for a photon gas in thermal equilibrium (grand canonical ensemble).It can be 0,finite or even infinite.The only thing we can compute is its average...

Daniel.

P.S.Equilibrium thermodynamics tells us that [itex] \mu [/itex] and [itex] N [/itex] are conjugate variables.
 

FAQ: Chemical potential (statistical physics)

What is chemical potential?

Chemical potential is a concept in statistical physics that measures the potential energy of a system due to the interactions between particles. It is a thermodynamic parameter that governs the tendency of particles to move from one region to another.

How is chemical potential related to temperature and pressure?

The chemical potential of a system is directly related to its temperature and pressure. As temperature increases, the average kinetic energy of particles increases, leading to a higher chemical potential. Similarly, as pressure increases, the volume of the system decreases, causing the particles to be more confined and resulting in a higher chemical potential.

What is the significance of chemical potential in phase transitions?

In phase transitions, the chemical potential plays a crucial role in determining the equilibrium state of a system. At the transition point, the chemical potential is equal in both phases, allowing for a smooth transition between the two phases. It also helps to predict the direction in which a phase transition will occur.

How is chemical potential calculated?

Chemical potential is typically calculated using the Gibbs free energy equation, where chemical potential is equal to the partial derivative of the Gibbs free energy with respect to the number of particles in the system. It can also be calculated using the Boltzmann distribution, which relates the chemical potential to the probability of finding a particle in a particular energy level.

What are some real-life applications of chemical potential?

Chemical potential has various applications in fields such as chemistry, biology, and materials science. It is used to understand and predict chemical reactions, determine the equilibrium states of chemical systems, and study the behavior of biological systems. It is also crucial in the design and development of new materials with specific properties.

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