entropy

Chemistry

(noun)

A thermodynamic property that is the measure of a system's thermal energy per unit temperature that is unavailable for doing useful work.

Related Terms

  • absolute zero
  • free energy of formation
  • thermalization
  • work
  • enthalpy
  • exergonic
  • endergonic
  • microstate

(noun)

A thermodynamic property that is the measure of a system's thermal energy per unit of temperature that is unavailable for doing useful work.

Related Terms

  • absolute zero
  • free energy of formation
  • thermalization
  • work
  • enthalpy
  • exergonic
  • endergonic
  • microstate
Physics

(noun)

A measure of how evenly energy (or some analogous property) is distributed in a system.

Related Terms

  • disorder
  • geothermal
  • asteroid
  • the first law of thermodynamics
  • thermodynamics
Statistics

(noun)

A measure which quantifies the expected value of the information contained in a message.

Related Terms

  • cumulant
  • empirical rule
Biology

(noun)

A measure of randomness and disorder in a system.

Related Terms

  • second law of thermodynamics
Economics

(noun)

A measure of the amount of information and noise present in a signal.

Examples of entropy in the following topics:

  • Struggle against entropy

  • Standard Entropy

    • The standard entropy of a substance (its entropy at 1 atmospheric pressure) helps determine if a reaction will take place spontaneously.
    • The standard entropy of a substance is its entropy at 1 atm pressure.
    • Some typical standard entropy values for gaseous substances include:
    • It is apparent that entropies generally increase with molecular weight.
    • There is an inverse correlation between the hardness of a solid and its entropy.
  • Order to Disorder

    • Entropy is a measure of disorder, so increased entropy means more disorder in the system.
    • Entropy is a measure of disorder.
    • There is a large increase in entropy in the process.
    • The mixing decreases the entropy of the hot water but increases the entropy of the cold water by a greater amount, producing an overall increase in entropy.
    • Entropy is a measure of disorder.
  • The Third Law

    • Entropy is related to the number of possible microstates, and with only one microstate available at zero kelvin the entropy is exactly zero.
    • Nernst proposed that the entropy of a system at absolute zero would be a well-defined constant.
    • This law provides an absolute reference point for the determination of entropy. ( diagrams the temperature entropy of nitrogen. ) The entropy (S) determined relative to this point is the absolute entropy represented as follows:
    • Temperature–entropy diagram of nitrogen.
    • Absolute value of entropy can be determined shown here, thanks to the third law of thermodynamics.
  • Changes in Energy

    • For isolated systems, entropy never decreases.
    • Increases in entropy correspond to irreversible changes in a system.
    • The entropy of a system is defined only if it is in thermodynamic equilibrium.
    • However, the entropy of the system of ice and water has increased more than the entropy of the surrounding room has decreased.
    • Ice melting in a warm room is a common example of increasing entropy.
  • Living Systems and Evolution

    • It is possible for the entropy of one part of the universe to decrease, provided the total change in entropy of the universe increases.
    • But it is always possible for the entropy of one part of the universe to decrease, provided the total change in entropy of the universe increases.
    • How is it possible for a system to decrease its entropy?
    • However, there is a large total increase in entropy resulting from this massive heat transfer.
    • Formulate conditions that allow decrease of the entropy in one part of the universe
  • Microstates and Entropy

    • With more available microstates, the entropy of a system increases.
    • As a result, entropy (denoted by S) is an expression of disorder or randomness.
    • With more available microstates, the entropy of a system increases.
    • This is the basis of an alternative (and more fundamental) definition of entropy:
    • Therefore, the entropy of a solid is less than the entropy of a liquid, which is much less than the entropy of a gas:
  • The Third Law of Thermodynamics and Absolute Energy

    • Specifically, the entropy of a pure crystalline substance at absolute zero temperature is zero.
    • Entropy is related to the number of possible microstates according to $S = k_Bln(\Omega)$, where S is the entropy of the system, kB is Boltzmann's constant, and Ω is the number of microstates (e.g. possible configurations of atoms).
    • The constant value (not necessarily zero) is called the residual entropy of the system.
    • The entropy determined relative to this point (absolute zero) is the absolute entropy.
    • The entropy (S) of a substance (compound or element) as a function of temperature (T).
  • Solutions and Entropy Changes

    • Chemists use the term "entropy" to denote this aspect of molecular randomness.
    • Entropy is indeed a fascinating, but somewhat confusing, topic.
    • In a similar manner entropy plays an important role in solution formation.
    • All these factors increase the entropy of the solute.
    • This is the same as saying that the entropy of the solute increases.
  • Changes in the Entropy of Surroundings

    • Irreversible reactions result in a change in entropy to the surroundings.
    • The heat from the surroundings (entropy) goes into the ice water and the ice melts.
    • The entropy of the ice water increases while the entropy of the surroundings decreases.
    • Distinguish whether or not entropy of surroundings changes in various reactions
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