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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...

The Second Law of Thermodynamics

The 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. Scientists refer to the measure of randomness or disorder within a system as entropy. High entropy means high disorder and low energy. To better understand entropy, think of a student’s bedroom. If no energy or work were put into it, the room would quickly become messy. It would exist in a very disordered state, one of high entropy. Energy must be...

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.

Atomic Spectroscopy: Effects of Temperature

Atomic Spectroscopy: Effects of Temperature

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Related Experiment Video

Updated: Dec 22, 2025

High-resolution Thermal Micro-imaging Using Europium Chelate Luminescent Coatings

High-resolution Thermal Micro-imaging Using Europium Chelate Luminescent Coatings

Published on: April 16, 2017

Temporal evolution of sample entropy in thermal lens system.

Vimal Raj¹, M S Swapna¹, K Satheesh Kumar²

¹Department of Optoelectronics and Department of Nanoscience and Nanotechnology, University of Kerala, Trivandrum 695581, Kerala, India.

Chaos (Woodbury, N.Y.)

|May 3, 2020

Summary

This study analyzes thermal lens signals to understand molecular dynamics in liquids. Findings reveal increased complexity and disorder, with entropy evolution mirroring refractive index changes.

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Submillisecond Conformational Changes in Proteins Resolved by Photothermal Beam Deflection

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Published on: February 18, 2014

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Last Updated: Dec 22, 2025

High-resolution Thermal Micro-imaging Using Europium Chelate Luminescent Coatings

High-resolution Thermal Micro-imaging Using Europium Chelate Luminescent Coatings

Published on: April 16, 2017

A Simple Dewar/Cryostat for Thermally Equilibrating Samples at Known Temperatures for Accurate Cryogenic Luminescence Measurements

A Simple Dewar/Cryostat for Thermally Equilibrating Samples at Known Temperatures for Accurate Cryogenic Luminescence Measurements

Published on: July 19, 2016

Submillisecond Conformational Changes in Proteins Resolved by Photothermal Beam Deflection

Submillisecond Conformational Changes in Proteins Resolved by Photothermal Beam Deflection

Published on: February 18, 2014

Area of Science:

Physical Chemistry
Thermodynamics
Nonlinear Optics

Background:

Photothermal phenomena induce thermal lensing in liquids due to temperature and refractive index changes.
Molecular dynamics govern these changes, impacting the system's thermodynamic properties like entropy.

Purpose of the Study:

To investigate the molecular dynamics underlying thermal lens formation using time series and phase portrait analysis.
To characterize the complexity, disorder, and persistence of the system's behavior.

Main Methods:

Time series analysis of the thermal lens signal.
Phase portrait analysis to visualize system dynamics.
Calculation of fractal dimension, sample entropy, and Hurst exponent.

Main Results:

The study quantifies increased complexity and disorder using fractal dimension and sample entropy.
Antipersistence in the system's behavior is indicated by the Hurst exponent.
Segmentation analysis shows evolving sample entropy and stochasticity over time.

Conclusions:

Temporal evolution of sample entropy correlates with temperature-dependent refractive index changes.
Phase portrait analysis supports the observed dynamic and stochastic nature of the system.