Gibbs Free Energy
Gibbs Free Energy - Related Videos
02:39
Gibbs Free Energy
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2020
One of the challenges of using the second law of thermodynamics to determine if a process is spontaneous is that it requires measurements of the entropy change for the system and the entropy change for the surroundings. An alternative approach involving a new thermodynamic property defined in terms of system properties only was introduced in the late nineteenth century by American mathematician Josiah Willard Gibbs. This new property is called the Gibbs free energy (G) (or simply the free...
01:29
The Reaction Gibbs Energy
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2026
The reaction Gibbs energy (ΔrG) is a crucial parameter that determines whether a reaction will occur spontaneously or not. It can be used to categorize reactions into two types: exergonic and endergonic.Exergonic reactions are those in which ΔrG is less than zero. This implies that these reactions can occur spontaneously without an external input of energy. In biological systems, a typical example of an exergonic reaction is the oxidation of carbohydrates. This reaction produces simple...
02:23
Gibbs Free Energy and Thermodynamic Favorability
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2023
The spontaneity of a process depends upon the temperature of the system. Phase transitions, for example, will proceed spontaneously in one direction or the other depending upon the temperature of the substance in question. Likewise, some chemical reactions can also exhibit temperature-dependent spontaneities. To illustrate this concept, the equation relating free energy change to the enthalpy and entropy changes for the process is considered: The spontaneity of a process, as reflected in the...
01:21
Free Energy
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2019
Free energy—abbreviated as G for the scientist Gibbs who discovered it—is a measurement of useful energy that can be extracted from a reaction to do work. It is the energy in a chemical reaction that is available after entropy is accounted for. Reactions that take in energy are considered endergonic and reactions that release energy are exergonic. Plants carry out endergonic reactions by taking in sunlight and carbon dioxide to produce glucose and oxygen. Animals, in turn, break down the...
02:58
Cell Potential and Free Energy
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2020
Thermodynamics of a Redox Reaction Thermodynamics is the branch of physics dealing with the relationship between heat and other forms of energy. In an electrochemical cell, chemical energy is converted into electrical energy. Thus, a link can be predicted between cell potential, free energy change, and the equilibrium constant for the reaction. Cell potential can also be measured as the oxidant or the reducing strength, and similar acid-base strength measures are reflected in equilibrium...
FAQs
The sign of ΔG compares the free energy of the initial and final states in the written reaction direction. A negative value corresponds to a decrease in free energy and favors that direction, while a positive value indicates that direction does not lower the system’s free energy. When ΔG equals zero, the system is at equilibrium.
The relationship ΔG = ΔH − TΔS shows that enthalpy and entropy make competing contributions. The enthalpy term describes heat-related energy changes, while the entropy term is weighted by temperature. Consequently, changing temperature can alter the balance between these contributions and may change the predicted direction or equilibrium behavior of a process.
Gibbs free energy connects thermodynamic favorability with composition, so changing the amounts or concentrations of reacting substances can alter which direction lowers the system’s free energy. This provides a basis for predicting shifts in reaction direction and equilibrium position rather than treating equilibrium as independent of the chemical mixture.
A basic evaluation identifies the relevant enthalpy change, entropy change, and temperature, then applies ΔG = ΔH − TΔS. The resulting value is interpreted for the reaction direction and equilibrium condition. Comparing values under different temperatures or compositions helps assess how operating conditions influence the process.
The concept applies across several areas of chemistry, including acid-base chemistry, redox reactions, and phase changes. It also supports analysis of biochemical pathways, where multiple chemical steps must be considered, and helps connect thermodynamic predictions with the direction and equilibrium position of chemically important processes.
In chemical engineering, free-energy analysis helps compare reaction conditions and identify directions that are thermodynamically favorable. This information can guide reaction design and the development of energy-efficient processes. Evaluating temperature and composition effects also helps engineers understand how operating choices may influence reaction behavior and equilibrium.