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Third Law of Thermodynamics

Third Law of Thermodynamics

A pure, perfectly crystalline solid possessing no kinetic energy (that is, at a temperature of absolute zero, 0 K) may be described by a single microstate, as its purity, perfect crystallinity,and complete lack of motion means there is but one possible location for each identical atom or molecule comprising the crystal (W = 1). According to the Boltzmann equation, the entropy of this system is zero.

Entropy

Entropy

Salt particles that have dissolved in water never spontaneously come back together in solution to reform solid particles. Moreover, a gas that has expanded in a vacuum remains dispersed and never spontaneously reassembles. The unidirectional nature of these phenomena is the result of a thermodynamic state function called entropy (S). Entropy is the measure of the extent to which the energy is dispersed throughout a system, or in other words, it is proportional to the degree of disorder of a...

Entropy

Entropy

The first law of thermodynamics is quantitatively formulated via an equation relating the internal energy of a system, the heat exchanged by it, and the work done on it. A quantitative formulation of the second law of thermodynamics leads to defining a state function, the entropy.
When an ideal gas expands isothermally, the disorder in the gas increases. From the molecular perspective, the gas molecules have more volume to move around in.
Consider an infinitesimal step in the expansion, which...

Entropy and the Second Law of Thermodynamics

Entropy and the Second Law of Thermodynamics

The second law of thermodynamics can be stated quantitatively using the concept of entropy. Entropy is the measure of disorder of the system.
The relation between entropy and disorder can be illustrated with the example of the phase change of ice to water. In ice, the molecules are located at specific sites giving a solid state, whereas, in a liquid form, these molecules are much freer to move. The molecular arrangement has therefore become more randomized. Although the change in average...

Second Law of Thermodynamics

Second Law of Thermodynamics

In the quest to identify a property that may reliably predict the spontaneity of a process, a promising candidate has been identified: entropy. Processes that involve an increase in entropy of the system (ΔS > 0) are very often spontaneous; however, examples to the contrary are plentiful. By expanding consideration of entropy changes to include the surroundings, a significant conclusion regarding the relation between this property and spontaneity may be reached. In thermodynamic models, the...

Second Law of Thermodynamics

Second Law of Thermodynamics

The Second Law of Thermodynamics states that entropy, or the amount of disorder in a system, increases each time energy is transferred or transformed. Each energy transfer results in a certain amount of energy that is lost—usually in the form of heat—that increases the disorder of the surroundings. This can also be demonstrated in a classic food web. Herbivores harvest chemical energy from plants and release heat and carbon dioxide into the environment. Carnivores harvest the...

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An Analog Macroscopic Technique for Studying Molecular Hydrodynamic Processes in Dense Gases and Liquids

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First-Principles Atomistic Thermodynamics and Configurational Entropy.

Christopher Sutton¹, Sergey V Levchenko²

¹Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC, United States.

Frontiers in Chemistry

|January 11, 2021

Summary

This study explores equilibrium statistical mechanics to predict material properties at realistic temperatures and pressures. Methods like atomistic thermodynamics and cluster expansion are discussed for calculating phase diagrams and defect concentrations.

Keywords:

atomistic thermodynamics method chemical potential cluster expansion configurational entropy phase diagram statistical mechanics

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Published on: December 4, 2017

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Computation of Atmospheric Concentrations of Molecular Clusters from ab initio Thermochemistry

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Area of Science:

Materials Science
Computational Chemistry
Statistical Mechanics

Background:

Functional materials operate under realistic conditions involving finite temperatures and interactions with atomic/molecular reservoirs.
Understanding material properties requires accounting for statistical effects from configurational sampling and particle exchange.

Purpose of the Study:

To elucidate the core concepts of equilibrium statistical mechanics.
To demonstrate the application of these concepts for predicting material behavior at realistic temperatures and pressures using atomistic thermodynamics.
To introduce methods for calculating phase diagrams and point defect concentrations.

Main Methods:

Equilibrium statistical mechanics principles.
Atomistic thermodynamics framework.
Calculation of configurational density of states.
Cluster expansion method for efficient energy evaluation.

Main Results:

Demonstrated prediction of material behavior under realistic conditions.
Introduced methods for calculating phase diagrams of bulk materials and surfaces.
Presented approaches for determining point defect concentrations.
Highlighted the utility of the cluster expansion method for evaluating energies of numerous configurations.

Conclusions:

Equilibrium statistical mechanics and atomistic thermodynamics are crucial for understanding materials at finite temperatures.
The discussed methods, including cluster expansion, enable accurate prediction of material properties, phase diagrams, and defect behavior.