Delta G of irreversible process

In summary, the conversation discusses the problem of calculating the Gibbs free energy for an irreversible process of protein unfolding. The person is unsure if the Gibbs free energy can be defined for an irreversible process and how to calculate it without an equilibrium constant. The other person suggests considering the initial and final states and following any path that leads to the same result, similar to the example of free expansion of a gas. They also mention the concept of state functions and suggest looking into the kinetics and Arrhenius activation energy for more information.
  • #1
arwelbath
10
0
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!
 
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  • #2
irreversible

I don't think I can help you fully with the problem.
But there is one idea that I have about calculating state variables like Gibbs' energy for irreversible processes.

It is not required for the system to undergo a reversible process. If your system has a definable state, then you just need to consider the initial and final states. The change in state functions will be the same whether the system undergoes a reversible or an irreversible change if the initial and final state are the same. So, you can follow any path which makes your calculations easy and leads to the same final condition. The result will be the same.

I saw such an example in the free expansion of a gas. Even though it is not a reversible process, we could calculate the change in entropy by taking into account only the initial and final states and some other process where it leads to the same result but was more easily calculable.

hope that helps!

spacetime
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1. What is Delta G of an irreversible process?

Delta G is a measure of the change in free energy during a chemical or physical process that is not reversible. It represents the maximum amount of work that can be extracted from a system during this process.

2. How is Delta G related to entropy?

Delta G is directly related to entropy, as it is defined as the change in free energy (Delta G) = change in enthalpy (Delta H) - temperature (T) x change in entropy (Delta S). This means that an increase in entropy will result in a decrease in Delta G, making the process more favorable.

3. Can Delta G be negative?

Yes, Delta G can be negative, which indicates that the process is spontaneous and releases energy. This means that the process is thermodynamically favorable and will occur without the need for external energy.

4. How is Delta G affected by temperature?

Delta G is directly proportional to temperature, meaning that as temperature increases, Delta G also increases. This is because an increase in temperature leads to an increase in entropy, which in turn increases Delta G.

5. What is the significance of Delta G in chemical reactions?

Delta G is an important factor in determining the spontaneity and energetics of a chemical reaction. A negative Delta G indicates that the reaction is exergonic, meaning it releases energy and is favorable, while a positive Delta G means the reaction is endergonic and requires energy to proceed. It also helps determine the equilibrium state of a reaction.

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