Exploring the Meaning of Helmholtz & Gibb Free Energy

[quantasham]

Hi guys,

We all know that Helmholtz free energy, Gibbs free energy and Enthalpy are defined by Legendre transformation.

For Enthalpy H=E+PV, I can understand it as the energy required to "displace the atmosphere" plus "creating the internal energy of system". What about Gibb free energy and Helmholtz free energy? What are their physical meaning?

 

[tiny-tim]

Hi quantasham!

Aren't they just the energy available for doing work?

So, for example, a chemical process is spontaneous at constant pressure and temperature if the Gibbs free energy would be decreased, and is spontaneous at constant volume and temperature if the Helmholtz free energy would be decreased.

So either Gibbs or Helmholtz free energy is like gravitational energy … a process will always go "downhill".

 

[charng]

Helmholtz and Gibbs free energies are important concepts in thermodynamics that help us understand the behavior of systems and the direction of chemical reactions. They are both defined by Legendre transformations, just like enthalpy, which means they are derived from other thermodynamic properties.

The Helmholtz free energy, also known as the Helmholtz function, is defined as the difference between a system's internal energy and its energy that is unavailable to do work. In other words, it represents the maximum amount of work that can be extracted from a closed system at constant temperature and volume. This makes it a useful quantity for studying systems that are not in equilibrium, as it tells us how much energy is available to do work.

On the other hand, the Gibbs free energy, also known as the Gibbs function, is defined as the difference between a system's enthalpy and the product of its temperature and entropy. It represents the maximum amount of work that can be extracted from a closed system at constant temperature and pressure. This makes it a useful quantity for studying systems that are in equilibrium, as it tells us the direction of spontaneous change and the stability of the system.

Overall, both Helmholtz and Gibbs free energies have important physical meanings in thermodynamics and are essential for understanding the behavior of systems and predicting the direction of chemical reactions. They are useful tools for scientists and engineers in various fields, such as chemistry, physics, and engineering.