Free energy and irreversible processes

[arwelbath]

Hi,
I'm working on a problem of the thermal stability of a protein. Conventionlly, people compare protein thermal stability in terms of the Gibbs free energy difference between the native and unfolded state. So if it reversibly falls apart, then for N <==> U, DG(N-U) is accessed from the classical equilibrium constant for the process. (DG = -RT ln K)

But, unfortunately my system unfolds irreversibly so that N --> U.

Is the gibbs free energy defined for an irreversible process? If so, how can it be calculated without an equilibrium constant? If it's not defined, is there an equilvalent quantity which can be used?

The best I can do so far is to look at the kinetics, which I've done and got an Arrhenius activation energy. Can I get any more information from this?

Please Help!

 

[cdirk11]

I'm pretty sure you can find delta G by using the equation
delta G = (delta H) - delta(TS) --> delta G = (Cp * delta T) - (TfSf - TiSi)

Hope this helps

 

[GSXR750]

Hi there,

Thank you for sharing your problem with us. The concept of free energy and irreversible processes is a fundamental topic in thermodynamics, and it can be a bit tricky to understand. In your case, it is important to keep in mind that the Gibbs free energy is defined for a system at equilibrium, where all processes are reversible. In irreversible processes, the system is not at equilibrium, and the concept of free energy becomes less relevant.

In thermodynamics, we use the concept of free energy to determine the direction of a spontaneous process. A process is spontaneous if it leads to a decrease in free energy of the system. In reversible processes, we can calculate the change in free energy using the equilibrium constant, as you have mentioned. However, in irreversible processes, the concept of equilibrium constant does not apply, and the change in free energy cannot be calculated in the same way.

So, to answer your question, the Gibbs free energy is not defined for irreversible processes. However, there are other quantities that can be used to describe the thermodynamic behavior of a system, such as the enthalpy, entropy, and activation energy. In your case, the Arrhenius activation energy that you have calculated can provide valuable information about the kinetics of the unfolding process.

I would suggest consulting with a thermodynamics expert or your instructor to see if there are any other approaches you can take to analyze the thermal stability of your protein. They may be able to provide you with more specific guidance and techniques to address your problem. I wish you the best of luck in your research.