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Related Concept Videos

Entropy02:39

Entropy

38.1K
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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Electrochemical Systems01:24

Electrochemical Systems

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Electrochemical systems provide a fascinating insight into the dynamic interplay of charged species within various phases. One notable example is the interaction between a membrane permeable to K⁺ ions but not to Cl⁻ ions, separating an aqueous KCl solution from pure water. As K⁺ ions diffuse through the membrane, they generate net charges on each phase, leading to a potential difference between them.Similarly, when a piece of Zn is immersed in an aqueous ZnSO₄ solution,...
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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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The Entropy as a State Function01:14

The Entropy as a State Function

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Consider an arbitrary process that moves between two specific states (A and B) in a cyclic manner. This process is reversible and broken down into smaller parts that each follow a Carnot cycle. A Carnot cycle has two isothermal (constant temperature) processes. During these processes, the ratio of the amount of heat transferred to their respective temperature remains constant. The other two processes in the Carnot cycle are also reversible but adiabatic, which means they occur without any heat...
104
Entropy Changes Accompanying Specific Processes01:21

Entropy Changes Accompanying Specific Processes

101
Entropy, a measure of disorder in a system, changes during phase transitions like freezing or boiling. At the transition temperature Ttrs, where two phases are in equilibrium, the phase transition is a reversible process. The entropy change can be calculated from a substance's enthalpy of transition using the equation ΔStrs = ΔtrsH /Ttrs.When a perfect gas expands isothermally from one volume to another, entropy increases logarithmically with volume. Conversely, isothermal compression...
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Calculation of First Law Quantities I01:25

Calculation of First Law Quantities I

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Thermodynamic systems undergoing phase transitions or temperature changes experience energy transfer in the form of heat (q) and work (w). For a reversible phase change at constant temperature (T) and pressure (p), the process involves no chemical reaction but results in energy exchange between distinct phases.The heat transferred during this process corresponds to the latent heat of transition, which is the amount of heat energy absorbed or released by a substance when it changes from one...
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Age-dependent Dynamics of Locomotion in Caenorhabditis elegans: A Lyapunov Exponent Analysis
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Calculation of a fluctuating entropic force by phase space sampling.

James T Waters1, Harold D Kim1

  • 1School of Physics, Georgia Institute of Technology and 832 State Street, Atlanta, Georgia 30332-0430.

Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics
|August 15, 2015
PubMed
Summary

A pinned polymer chain

Area of Science:

  • Polymer physics
  • Statistical mechanics
  • Computational biophysics

Background:

  • Entropic forces in polymers are understood on average.
  • The distribution of instantaneous forces from pinned polymers is largely unknown.
  • Understanding force distributions is crucial for polymer dynamics.

Purpose of the Study:

  • To develop methods for sampling the equilibrium distribution of instantaneous forces.
  • To investigate the force distribution of terminally pinned polymers.
  • To elucidate the mechanistic origin of entropic forces.

Main Methods:

  • Introduced two phase space sampling methods.
  • Used Lagrangian dynamics to calculate constraint forces.
  • Simulated freely jointed polymer chains in space and on a surface.

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Main Results:

  • Developed methods to produce equilibrium force distributions.
  • Force distributions are highly asymmetric, showing both tensile and compressive forces.
  • The mean force (entropic force) is not the most probable force, even for long chains.

Conclusions:

  • The study reveals the asymmetric nature of polymer forces.
  • Provides computational tools for unbiased phase space sampling of constrained systems.
  • Offers new insights into the fundamental nature of entropic forces.