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Calculating Standard Free Energy Changes

Calculating Standard Free Energy Changes

The free energy change for a reaction that occurs under the standard conditions of 1 bar pressure and at 298 K is called the standard free energy change. Since free energy is a state function, its value depends only on the conditions of the initial and final states of the system. A convenient and common approach to the calculation of free energy changes for physical and chemical reactions is by use of widely available compilations of standard state thermodynamic data. One method involves the...

Gibbs Free Energy

Gibbs Free Energy

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...

An Introduction to Free Energy

An Introduction to Free Energy

How can we compare the energy that releases from one reaction to that of another reaction? We use a measurement of free energy to quantitate these energy transfers. Scientists call this free energy Gibbs free energy (abbreviated with the letter G) after Josiah Willard Gibbs, the scientist who developed the measurement. According to the second law of thermodynamics, all energy transfers involve losing some energy in an unusable form such as heat, resulting in entropy. Gibbs free energy...

Gibbs Free Energy and Thermodynamic Favorability

Gibbs Free Energy and Thermodynamic Favorability

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:

Free Energy Changes for Nonstandard States

Free Energy Changes for Nonstandard States

The free energy change for a process taking place with reactants and products present under nonstandard conditions (pressures other than 1 bar; concentrations other than 1 M) is related to the standard free energy change according to this equation:

Free Energy

Free Energy

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...

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Computation of Atmospheric Concentrations of Molecular Clusters from ab initio Thermochemistry

Computation of Atmospheric Concentrations of Molecular Clusters from ab initio Thermochemistry

Published on: April 8, 2020

An efficient, path-independent method for free-energy calculations.

Michael D Tyka¹, Anthony R Clarke, Richard B Sessions

¹Department of Biochemistry, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, UK. m.tyka@bris.ac.uk

The Journal of Physical Chemistry. B

|August 25, 2006

Summary

This study introduces a novel, path-independent method for calculating free-energy differences. It simplifies complex calculations by transforming states, aiding in understanding peptide structural propensities.

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Area of Science:

Computational chemistry
Molecular dynamics
Biophysics

Background:

Classical free-energy calculations require defining integration paths, which can be computationally expensive and problematic for non-overlapping states.
Calculating free-energy differences is crucial for understanding molecular behavior and predicting structural stability.

Purpose of the Study:

To develop a novel, path-independent method for calculating free-energy differences.
To apply this method to determine side-chain entropies in a beta-hairpin-forming peptide and assess its impact on structural propensities.

Main Methods:

The novel method transforms end states into reference states where vibrational entropy is the sole component of total entropy.
This transformation allows for direct computation of relative free energy, bypassing the need for integration paths.

Main Results:

The method was successfully applied to calculate side-chain entropies of a beta-hairpin-forming peptide across various backbone conformations.
Analysis revealed that stable low-free-energy conformations result from a balance between enthalpic gains and entropic losses.

Conclusions:

The developed path-independent method offers a computationally efficient alternative for calculating free-energy differences, especially for distant states.
This approach is valuable for elucidating the factors governing structural propensities in peptides and other biomolecules.