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Thermodynamic Potentials

Thermodynamic Potentials

Thermodynamic potentials are state functions that are extremely useful in analyzing a thermodynamic system. They have dimensions of energy. The four important thermodynamic potentials are internal energy, enthalpy, Helmholtz free energy, and Gibbs free energy. These thermodynamic potentials can be expressed using two of the following variables: pressure, volume, temperature, and entropy. These two variables are expressed as the rate of change of the thermodynamic potential with respect to other...

Thermal Electrocyclic Reactions: Stereochemistry

Thermal Electrocyclic Reactions: Stereochemistry

The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.

Effects of Temperature on Free Energy

Effects of Temperature on Free Energy

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:

Induced Electric Dipoles

Induced Electric Dipoles

A permanent electric dipole orients itself along an external electric field. This rotation can be quantified by defining the potential energy because the external torque does work in rotating it. Then, the potential energy is minimum at the parallel configuration and maximum at the antiparallel configuration. While the former is a stable equilibrium, the latter is an unstable equilibrium.
Since the absolute value of potential energy holds no physical meaning, its zero value can be chosen as per...

Le Chatelier's Principle: Changing Temperature

Le Chatelier's Principle: Changing Temperature

Consistent with the law of mass action, an equilibrium stressed by a change in concentration will shift to re-establish equilibrium without any change in the value of the equilibrium constant, K. When an equilibrium shifts in response to a temperature change, however, it is re-established with a different relative composition that exhibits a different value for the equilibrium constant.
To understand this phenomenon, consider the elementary reaction:

Thermodynamics: Chemical Potential and Activity

Thermodynamics: Chemical Potential and Activity

The effective concentration of a species in a solution can be expressed precisely in terms of its activity. Activity considers the effect of electrolytes present in the vicinity of the species of interest and depends on the ionic strength of the solution. The activity of a species is expressed as the product of molar concentration and the activity coefficient of the species.
The thermodynamic equilibrium constant is more accurately defined in terms of activity rather than concentration.

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Updated: Jun 21, 2025

Synthesis of Non-uniformly Pr-doped SrTiO3 Ceramics and Their Thermoelectric Properties

Synthesis of Non-uniformly Pr-doped SrTiO3 Ceramics and Their Thermoelectric Properties

Published on: August 15, 2015

Orientational Effects and Molecular-Scale Thermoelectricity Control.

Turki Alotaibi¹, Maryam Alshahrani², Majed Alshammari¹

¹Department of Physics, College of Science, Jouf University, Sakaka 72388, Saudi Arabia.

|July 15, 2024

Summary

Researchers explored molecular orientation effects in asymmetric junctions. They found that molecule orientation influences the Seebeck coefficient, enabling potential applications in molecular thermoelectric energy generators.

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Synthesis of Non-uniformly Pr-doped SrTiO3 Ceramics and Their Thermoelectric Properties

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Area of Science:

Molecular electronics
Thermoelectric energy conversion
Quantum transport phenomena

Background:

The orientational effect in molecular junctions is crucial for controlling charge transport.
Asymmetric junctions are key to observing directional electronic properties.
Understanding molecular orientation is vital for designing efficient molecular devices.

Purpose of the Study:

To theoretically investigate the orientational effect in asymmetric molecular junctions.
To demonstrate how molecular orientation impacts the Seebeck coefficient.
To explore the potential for bithermoelectricity in molecular systems.

Main Methods:

Theoretical investigation of molecular-scale junctions.
Utilizing asymmetric molecules with distinct terminal end groups.
Constructing doubly asymmetric junctions (e.g., Au/Zn-TPP+M/Au).

Main Results:

Demonstrated sign fluctuation of Seebeck coefficients based on molecular orientation.
Identified bithermoelectric behavior in anthracene-based compounds with pyridyl and thioacetate groups.
Confirmed the influence of strong anchor groups on thermoelectric properties.

Conclusions:

Molecular orientation significantly affects thermoelectric properties in asymmetric junctions.
Bithermoelectricity can be achieved by controlling molecular orientation.
This work paves the way for enhanced molecular thermoelectric energy generators (TEGs).