entropy
Chemistry
Physics
(noun)
A measure of how evenly energy (or some analogous property) is distributed in a system.
Statistics
(noun)
A measure which quantifies the expected value of the information contained in a message.
Biology
(noun)
A measure of randomness and disorder in a system.
Economics
(noun)
A measure of the amount of information and noise present in a signal.
Examples of entropy in the following topics:
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Struggle against entropy
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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.
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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.
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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.
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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.
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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
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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:
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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).
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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.
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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