Understanding Free Gibbs Energy: The Role of TΔS in Thermodynamics

In summary, the conversation discusses the meaning of TΔS in the free Gibbs energy equation and its interpretation as either energy lost or unavailable to do work. Some books suggest TΔS as energy lost or dispersal energy, while others see it as useful energy for work. The physical interpretation of TΔS is heat entering the system from the environment that can be used for additional work.
  • #1
david22
8
0
I´m having serious problems with free gibbs energy equation. My main problem is that i don't know the meaning of TΔS that appears in free gibbs formula. I know that S is entropy and T temperature; but some books say that TΔS is energy lost or dispersal energy; energy unavailable to do work; but for example, let's say that the sistem loses 30 joules of heat so ΔH will be negative because it is an exothermic reaction; and let's say that the ΔS is positive at T=25°ℂ and let's say that TΔS = 30 joules. So if we add this numers in the equation -30J - 30J = -60J so this number is the energy useful to do work so this means that TΔS is also energy that is useful to do work, so my question is why some books say that this is energy unable to do work? and if you can give me a physical interpretation of TΔS ( what kind of energy is it?) i would appreciate it
 
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  • #2
Hi David, welcome to PF!

Could you please provide quotes for the statement? Just saying "some books say that" is not very helpful (sometimes, conetxt is everything).

If [itex]\Delta S[/itex] is positive, it usually means that heat is entering the system from the environment, which can indeed be used for additional work.
 

1. What is free Gibbs energy and why is it important in thermodynamics?

Free Gibbs energy, also known as Gibbs free energy, is a thermodynamic quantity that represents the amount of energy available to do useful work in a system. It takes into account both the enthalpy (heat content) and entropy (degree of disorder) of a system, making it a valuable measure of a system's spontaneity and stability.

2. How is free Gibbs energy related to the concept of TΔS?

In thermodynamics, the change in free Gibbs energy (ΔG) is equal to the product of temperature (T) and the change in entropy (ΔS), or TΔS. This relationship is known as the Gibbs-Helmholtz equation and it explains the role of TΔS in determining the spontaneity of a reaction. A positive value for TΔS indicates that the reaction is spontaneous, while a negative value indicates a non-spontaneous process.

3. Can free Gibbs energy be used to predict whether a reaction will occur?

Yes, the free Gibbs energy change (ΔG) can be used to predict whether a reaction will occur under certain conditions. If ΔG is negative, the reaction is spontaneous and will occur without the need for additional energy input. On the other hand, a positive value for ΔG indicates a non-spontaneous reaction that will only occur with the input of energy.

4. How does temperature affect free Gibbs energy?

The relationship between temperature and free Gibbs energy is described by the Gibbs-Helmholtz equation. As temperature increases, the value of TΔS also increases, making it more likely for a reaction to be spontaneous. Additionally, at high temperatures, the entropic contribution (ΔS) can outweigh the enthalpic contribution (ΔH) to the overall ΔG value, leading to a negative ΔG and a spontaneous reaction.

5. Are there any limitations to using free Gibbs energy in thermodynamics?

While free Gibbs energy is a useful quantity in thermodynamics, it does have some limitations. It assumes that reactions occur at constant temperature and pressure, and that the system is in equilibrium. In reality, many reactions occur under non-equilibrium conditions and may be affected by factors such as concentration, pressure, and catalysts. Additionally, free Gibbs energy calculations may become more complex for multi-component systems or non-ideal solutions.

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