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Related Concept Videos

Absolute Entropies and the Third Law of Thermodynamics01:23

Absolute Entropies and the Third Law of Thermodynamics

Ludwig Edward Boltzmann developed a definition for entropy, which stated that absolute entropy is proportional to the natural logarithm of the number of possible combinations of particles. Entropy stands alone among state functions as the only one whose absolute values can be determined.Consider a gas sample confined to a container. As the container expands, the energy levels of gas molecules become more closely spaced. This increases the number of available energy states, thereby increasing...
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The first law of thermodynamics establishes that the change in internal energy of a system is given by ΔU = q + w, where q is the heat exchanged, and w is the work performed. For a perfect gas, both internal energy (U) and enthalpy (H) depend solely on temperature. Consequently, for any change of state, whether reversible or irreversible, the internal energy change is determined by integrating the heat capacity at constant volume, and the enthalpy change by integrating the heat capacity at...
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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...
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An Analog Macroscopic Technique for Studying Molecular Hydrodynamic Processes in Dense Gases and Liquids
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Published on: December 4, 2017

Beyond quantum microcanonical statistics.

Barbara Fresch1, Giorgio J Moro

  • 1Dipartimento di Science Chimiche, Università di Padova, via Marzolo 1, 35131 Padova, Italy. barbara.fresch@unipd.it

The Journal of Chemical Physics
|February 10, 2011
PubMed
Summary
This summary is machine-generated.

This study introduces a novel statistical framework for isolated molecular systems, bridging quantum mechanics and thermodynamics. It enables the emergence of typical thermodynamic properties, like energy and entropy, in macroscopic systems.

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Area of Science:

  • Quantum Mechanics
  • Statistical Mechanics
  • Thermodynamics
  • Molecular Systems

Background:

  • Molecular systems are typically described by quantum pure states (wavefunctions) or mixed states (density matrices) for thermal equilibrium.
  • Current frameworks face challenges in unifying quantum descriptions with macroscopic thermodynamic behavior.

Purpose of the Study:

  • To present an alternative theoretical framework for molecular systems using statistical analysis of wavefunctions.
  • To develop a formalism that ensures the emergence of thermodynamic properties in the macroscopic limit.
  • To reconcile quantum mechanics with equilibrium thermodynamics without system-specific constraints.

Main Methods:

  • Statistical analysis of possible wavefunctions for isolated systems.
  • Introduction of a probability distribution for quantum constants of motion.
  • Analogy with classical ergodic theory for wavefunction time evolution.

Main Results:

  • A workable formalism is presented for deriving thermodynamic functions (internal energy, entropy) in the large size limit.
  • Macroscopic properties are identifiable independent of the specific quantum state realization.
  • The canonical statistics for subsystems is recovered generally.

Conclusions:

  • The developed formalism provides a unified description of material systems consistent with equilibrium thermodynamics.
  • It offers a new perspective on the quantum-to-classical transition in thermodynamics.
  • The approach is broadly applicable, irrespective of the system's constituents and interactions.