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Related Concept Videos

Entropy01:18

Entropy

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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...
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Entropy Change in Reversible Processes01:10

Entropy Change in Reversible Processes

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In the Carnot engine, which achieves the maximum efficiency between two reservoirs of fixed temperatures, the total change in entropy is zero. The observation can be generalized by considering any reversible cyclic process consisting of many Carnot cycles. Thus, it can be stated that the total entropy change of any ideal reversible cycle is zero.
The statement can be further generalized to prove that entropy is a state function. Take a cyclic process between any two points on a p-V diagram.
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Enthalpy02:59

Enthalpy

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Chemists ordinarily use a property known as enthalpy (H) to describe the thermodynamics of chemical and physical processes. Enthalpy is defined as the sum of a system’s internal energy (E) and the mathematical product of its pressure (P) and volume (V):
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Hess's Law03:40

Hess's Law

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There are two ways to determine the amount of heat involved in a chemical change: measure it experimentally, or calculate it from other experimentally determined enthalpy changes. Some reactions are difficult, if not impossible, to investigate and make accurate measurements for experimentally. And even when a reaction is not hard to perform or measure, it is convenient to be able to determine the heat involved in a reaction without having to perform an experiment.
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Enthalpy of Solution02:39

Enthalpy of Solution

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There are two criteria that favor, but do not guarantee, the spontaneous formation of a solution:
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Gibbs Free Energy and Thermodynamic Favorability02:23

Gibbs Free Energy and Thermodynamic Favorability

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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:
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Unraveling Entropic Rate Acceleration Induced by Solvent Dynamics in Membrane Enzymes
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Enthalpy-entropy compensation in the slow Arrhenius process.

Erik Thoms1, Simone Napolitano1

  • 1Laboratory of Polymer and Soft Matter Dynamics, Experimental Soft Matter and Thermal Physics (EST), Université libre de Bruxelles (ULB), Brussels 1050, Belgium.

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The Meyer-Neldel compensation law applies to polymer relaxation processes. This indicates that overcoming energy barriers involves multiple low-energy excitations, explaining multiphonon relaxation.

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Area of Science:

  • Physical Chemistry
  • Polymer Science
  • Materials Science

Background:

  • The Meyer-Neldel compensation law describes a relationship between entropy and enthalpy in thermally activated processes.
  • This law is widely observed in chemical reactions and other physical phenomena.
  • A slow Arrhenius process, a microscopic relaxation mode, has been identified in liquid and glassy states.

Purpose of the Study:

  • To investigate the applicability of the Meyer-Neldel compensation law to the slow Arrhenius process in polymers.
  • To understand the underlying mechanisms of relaxation and equilibration in polymer systems.

Main Methods:

  • Analysis of 31 different polymer systems.
  • Examination of the slow Arrhenius process, a microscopic relaxation mode.
  • Application of the multiexcitation entropy model for interpretation.

Main Results:

  • The Meyer-Neldel compensation law was observed in the slow Arrhenius process across various polymer systems.
  • This behavior suggests a connection between entropic and enthalpic components of energy barriers in polymers.
  • The findings support the multiexcitation entropy model for relaxation processes.

Conclusions:

  • The Meyer-Neldel compensation law is a relevant principle for understanding polymer relaxation dynamics.
  • Overcoming significant energy barriers in polymers involves numerous low-energy excitations, characteristic of multiphonon relaxation.
  • The multiexcitation entropy model provides a framework for interpreting these complex relaxation mechanisms.