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What Is Heat? Can Heat Capacities Be Negative?

In the absence of work, the exchange of heat of a sample of matter corresponds to the change of its internal energy, given by the kinetic energy of random translational motion of all its constituent atoms or molecules relative to the center of mass of the sample, plus the excitation of quantum state...

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Autor principal: Roduner, Emil
Formato: Online Artículo Texto
Lenguaje:English
Publicado: MDPI 2023
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10048101/
https://www.ncbi.nlm.nih.gov/pubmed/36981417
http://dx.doi.org/10.3390/e25030530
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author Roduner, Emil
author_facet Roduner, Emil
author_sort Roduner, Emil
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description In the absence of work, the exchange of heat of a sample of matter corresponds to the change of its internal energy, given by the kinetic energy of random translational motion of all its constituent atoms or molecules relative to the center of mass of the sample, plus the excitation of quantum states, such as vibration and rotation, and the energy of electrons in excess to their ground state. If the sample of matter is equilibrated it is described by Boltzmann’s statistical thermodynamics and characterized by a temperature T. Monotonic motion such as that of the stars of an expanding universe is work against gravity and represents the exchange of kinetic and potential energy, as described by the virial theorem, but not an exchange of heat. Heat and work are two distinct properties of thermodynamic systems. Temperature is defined for the radiative cosmic background and for individual stars, but for the ensemble of moving stars neither temperature, nor pressure, nor heat capacities are properly defined, and the application of thermodynamics is, therefore, not advised. For equilibrated atomic nanoclusters, in contrast, one may talk about negative heat capacities when kinetic energy is transformed into potential energy of expanding bonds.
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spelling pubmed-100481012023-03-29 What Is Heat? Can Heat Capacities Be Negative? Roduner, Emil Entropy (Basel) Opinion In the absence of work, the exchange of heat of a sample of matter corresponds to the change of its internal energy, given by the kinetic energy of random translational motion of all its constituent atoms or molecules relative to the center of mass of the sample, plus the excitation of quantum states, such as vibration and rotation, and the energy of electrons in excess to their ground state. If the sample of matter is equilibrated it is described by Boltzmann’s statistical thermodynamics and characterized by a temperature T. Monotonic motion such as that of the stars of an expanding universe is work against gravity and represents the exchange of kinetic and potential energy, as described by the virial theorem, but not an exchange of heat. Heat and work are two distinct properties of thermodynamic systems. Temperature is defined for the radiative cosmic background and for individual stars, but for the ensemble of moving stars neither temperature, nor pressure, nor heat capacities are properly defined, and the application of thermodynamics is, therefore, not advised. For equilibrated atomic nanoclusters, in contrast, one may talk about negative heat capacities when kinetic energy is transformed into potential energy of expanding bonds. MDPI 2023-03-19 /pmc/articles/PMC10048101/ /pubmed/36981417 http://dx.doi.org/10.3390/e25030530 Text en © 2023 by the author. https://creativecommons.org/licenses/by/4.0/Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).
spellingShingle Opinion
Roduner, Emil
What Is Heat? Can Heat Capacities Be Negative?
title What Is Heat? Can Heat Capacities Be Negative?
title_full What Is Heat? Can Heat Capacities Be Negative?
title_fullStr What Is Heat? Can Heat Capacities Be Negative?
title_full_unstemmed What Is Heat? Can Heat Capacities Be Negative?
title_short What Is Heat? Can Heat Capacities Be Negative?
title_sort what is heat? can heat capacities be negative?
topic Opinion
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10048101/
https://www.ncbi.nlm.nih.gov/pubmed/36981417
http://dx.doi.org/10.3390/e25030530
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