Activity and chemical potential

In summary: Basic theory and methods.In summary, the conversation is about understanding the difference between chemical potential and activity, and why it is important to know the activities of certain species in material growth. The chemical potential of a species is a function of its activity, which is a measure of its abundance. In the dilute limit, activity is equivalent to gas partial pressure or solute concentration, but in the high abundance limit, there is a distinction due to interactions between particles. Knowing activities is important in various contexts, such as predicting corrosion rates or studying adsorption on surfaces. Further reading on electrochemistry or statistical mechanics may provide a deeper understanding of this concept.
  • #1
marie2010
36
0
hi,
can someone help me in understanding the difference between chemical potential and activity?
Why it is important to know/determine activities of certain species in material growth? Given that activity is dimensionless quantity, what is it measuring?

Also, what is the activity of pure solids, liquids, and gases? Is it important to specify temperature, pressure, etc. when asking for species' activites?

Thank you in advance.
 
Physics news on Phys.org
  • #2
Roughly speaking, the chemical potential of species X is a function of its activity. In the dilute limit ,i.e, when the particles of species X do not "see" each other, the activity is simply the partial pressure of the gas or the concentration of solid species in aqueous solution. On the other hand if the particles of species X can "see" each other (in other words can interact with each other), then we express this effect emperically by specifiying activity coefficient. As an example, the activity of dissolved solid in aquous solution would be concentration x the activity coefficient.
 
  • #3
Thanks for the reply. I am still, however, confused about the activity concept.
So, does it measure the strength of interaction of the species?
Why is it important to know it?

Thanks.
 
  • #4
The activity is a measure of the abundance of the species. What I described in my previous post is the how the notion of reactivity is distinct from the familiar concepts of gas partial pressure and solute concentration. I summarize again that in the dilute limit there is no distinction, while in the high abundance limit (interacting species) there is a distinction.

It is importance depends on the context. For example, a corrosion scientist would care about the activity of chloride ions in a solution to be able to predict the corrosion rate of a metal. Another example, a surface scientist would care about the activity of oxygen gas to study its adsorption on metal surfaces.

I recommend reading an introductory text in electrochemistry (or may be corrosion science or physical chemistry) to understand the definition. If you want to go one step deeper , you can read a statitichal mechanics text to see in general how interactions between particles lead to deviation from ideal behavior.

Edit: I checked Wikipedia page on activity(chemistry) and it seems also a good introduction to the topic.
 
Last edited:
  • #5
Maybe you would find the following book valuable:

Klotz, Rosenberg, Chemical Thermodynamics
 

1. What is activity and chemical potential?

Activity and chemical potential are two concepts used in chemistry to describe the behavior of molecules in a system. Activity refers to the effective concentration of a substance, taking into account any interactions with other molecules in the system. Chemical potential is a measure of the energy of a substance and its tendency to move from one location to another.

2. How are activity and chemical potential related?

Activity and chemical potential are closely related, as the chemical potential of a substance is dependent on its activity. In general, the higher the activity of a substance, the higher its chemical potential will be. This means that a substance with a higher activity will have a greater tendency to move from one location to another.

3. What factors affect activity and chemical potential?

There are several factors that can affect the activity and chemical potential of a substance. These include temperature, pressure, and the presence of other substances in the system. Changes in these factors can alter the activity and chemical potential of a substance, and therefore its behavior within the system.

4. How is activity different from concentration?

Activity and concentration are related, but they are not the same thing. Concentration refers to the amount of a substance in a given volume or mass of a solution, while activity takes into account the interactions of the substance with other molecules in the system. Therefore, two solutions with the same concentration may have different activities depending on the other substances present.

5. How is the activity coefficient calculated?

The activity coefficient is a measure of how much the activity of a substance deviates from its ideal behavior. It is calculated by dividing the observed activity by the ideal activity, which is the activity that would be expected if the substance followed the ideal behavior of a dilute solution. The activity coefficient can vary based on factors such as temperature, pressure, and the nature of the substance itself.

Similar threads

Replies
1
Views
912
  • Chemistry
Replies
2
Views
781
  • Atomic and Condensed Matter
Replies
3
Views
1K
  • Introductory Physics Homework Help
Replies
4
Views
730
  • Advanced Physics Homework Help
Replies
8
Views
910
  • Materials and Chemical Engineering
Replies
2
Views
1K
  • Introductory Physics Homework Help
Replies
3
Views
821
  • Materials and Chemical Engineering
Replies
4
Views
2K
  • Materials and Chemical Engineering
Replies
6
Views
7K
  • Atomic and Condensed Matter
Replies
2
Views
3K
Back
Top