entropy

(noun)

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

Related Terms

Examples of entropy in the following topics:

  • 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.

  • 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

  • What is Entropy?

    • In this and following Atoms, we will study entropy.
    • We can see how entropy is defined by recalling our discussion of the Carnot engine.
    • The SI unit for entropy is joules per kelvin (J/K).
    • Entropy is a property of state.
    • Calculate the total change in entropy for a system in a reversible process

  • Heat Death

    • The entropy of the universe is constantly increasing and is destined for thermodynamic equilibrium, called the heat death of the universe.
    • As entropy increases, less and less energy in the universe is available to do work.
    • Since the universe is a closed system, the entropy of the universe is constantly increasing, and so the availability of energy to do work is constantly decreasing.
    • Either way, the universe is destined for thermodynamic equilibrium—maximum entropy.
    • Calculations of black holes suggest that entropy can easily continue for at least 10100 years.

  • Problems

    • Show that the entropy of the fluid increases as it passes through a shock.
    • Hint: the equation of state of an isentropic fluid is $P = K\rho^\gamma$ where the value of $K$ increases with increasing entropy.

  • Adiabatic Processes

    • Previously, we learned about the third law of thermodynamics, which states: the entropy of a perfect crystal at absolute zero is exactly equal to zero.
    • Assuming an entropy difference at absolute zero, T=0 could be reached in a finite number of steps.
    • However, going back to the third law, at T=0 there is no entropy difference, and therefore an infinite number of stepswould be needed for this process (illustrated in ).
    • Temperature-Entropy diagram.

  • Absolute Zero

    • Absolute zero is the coldest possible temperature; formally, it is the temperature at which entropy reaches its minimum value.
    • Formally, it is the temperature at which entropy reaches its minimum value.

  • Ideal Fluids

    • In the ideal fluid, no heat is transferred between different parts of the fluid, so if we denote $s$ as the entropy per unit rest mass we have
    • for a bunch of fluid; therefore, we also have a continuity equation for the entropy

  • Stastical Interpretation of Entropy

    • So even if you start with an orderly state, there is a strong tendency to go from order to disorder, from low entropy to high entropy.
    • (b) With energy transfer, the gas can be forced into one corner and its entropy greatly reduced.
    • But left alone, it will spontaneously increase its entropy and return to the normal conditions, because they are immensely more likely.