Why is free energy "free"?

Name: Problem 22, Chapter 18: Chemistry A Molecular Approach
Uploaded: 2019-06-23T21:30:46-08:00
Duration: 1 min 52 s
Channel: Lucas Pressley
Description: Why is free energy "free"?

Key Concepts

Gibbs Free Energy

Gibbs free energy is a thermodynamic potential that represents the amount of energy available to do work in a system at constant temperature and pressure. It is defined by the equation G = H - TS, where H is enthalpy and TS is the product of temperature and entropy. The term 'free' indicates that it is the energy remaining after subtracting the energy tied up in disorder, or entropy, and thus is available for performing work in chemical and physical processes.

Helmholtz Free Energy

Helmholtz free energy applies to systems held at constant volume and temperature. It is defined by the relation A = U - TS, where U is the internal energy of the system and TS represents the energy unavailable for work due to entropy. This formulation highlights the concept of 'free' energy as the portion of total energy that can be utilized to do work.

Energy Availability

The notion of 'free' energy in both Gibbs and Helmholtz formulations emphasizes the idea of available energy. Free energy is not free in the sense of costless, but rather refers to the energy that is not 'bound' or 'tied up' by entropy. It quantifies the usable energy that can be harnessed to perform work, making it central to understanding the spontaneity of processes.

Entropy

Entropy is a measure of disorder or randomness within a system. In the context of free energy, a portion of a system's total energy is 'consumed' by entropy, which reduces the energy available to perform work. Understanding entropy is crucial to the concept of free energy, as it explains why not all energy can be applied to work, hence the designation of the remaining energy as 'free.'

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