Gibbs free energy

Gibbs energy, also known as Gibbs free energy, is a vital concept in thermodynamics. It is a thermodynamic potential used to calculate the maximum amount of useful work a system can perform. This work must be something other than pressure-volume work, such as electrical work. The calculation applies to a closed system held at constant temperature and pressure. A closed system can exchange heat and work with its surroundings, but it cannot exchange matter. Understanding this energy helps scientists predict if a chemical process will occur naturally.

To understand the mechanism, we must look at the mathematical formula. The Gibbs energy, represented by the symbol G, is calculated using several parts. It equals the enthalpy of the system minus the product of temperature and entropy. Enthalpy, or H, represents the total heat content of the system. Entropy, or S, measures the spread or disorder of energy. Temperature, or T, is measured in Kelvin. The formula is G = H - TS. By looking at the change in this value, known as delta G, we can see how much energy is available.

When a system undergoes a change, we focus on the change in Gibbs energy, or delta G. If delta G is negative, the process is called an exergonic process. This means the reaction is thermodynamically favorable and can happen spontaneously. If delta G is positive, the reaction is called an endergonic process. In this case, the reaction is not spontaneous. To make an endergonic reaction happen, you must add energy from the outside, such as electrical work. This added energy must be greater than the positive delta G value.

This energy concept has a rich history in science. An American scientist named Josiah Willard Gibbs developed these ideas in the 1870s. He originally called this concept "available energy." In 1873, he published a paper using geometrical representations to explain thermodynamic properties. He used three-dimensional graphs to study how substances interact. In 1876, he published his major work, "On the Equilibrium of Heterogeneous Substances." This book provided a deep analysis of multi-phase chemical systems.

Gibbs' work helped replace the older term "affinity." Earlier chemists used affinity to describe the force driving chemical reactions. Over sixty years, free energy became the standard term. In 1923, a textbook by Gilbert N. Lewis and Merle Randall helped spread this usage. Interestingly, the term "free" is sometimes dropped in modern science. In 1988, an IUPAC meeting recommended using just "Gibbs energy." They wanted the name to be more precise, as "free" refers specifically to energy available for non-pressure-volume work.

There are surprising facts about how these energy changes appear in real life. For example, consider the transformation of a diamond into graphite. At 25 degrees Celsius and 1 atmosphere of pressure, this reaction has a negative delta G. This means the change is thermodynamically favorable. However, you will never see a diamond turn into graphite on your desk. The reaction is simply too slow because it has a very high activation energy. This shows that a favorable energy change does not always mean a fast reaction.

Gibbs energy connects to many important scientific fields. It is used to determine the voltage of an electrochemical cell. This is essential for understanding how batteries work and provide power. It also helps scientists find the equilibrium constant for reversible reactions. This constant tells us how a chemical mixture settles over time. Furthermore, scientists can use "coupling" to drive reactions. They can pair an unfavorable endergonic reaction with a favorable exergonic one. This allows the total entropy change of the universe to remain zero or positive.