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Entropy is an extensive property of a thermodynamic system, which means it depends on the amount of matter that is present. In equations, the symbol for entropy is the letter S. It has SI units of joules per kelvin (J⋅K −1) or kg⋅m 2 ⋅s −2 ⋅K −1. Examples of Entropy. Here are several examples of entropy:
In classical thermodynamics, the entropy of a system is defined if and only if it is in a thermodynamic equilibrium (though a chemical equilibrium is not required: for example, the entropy of a mixture of two moles of hydrogen and one mole of oxygen in standard conditions is well-defined).
The second law of thermodynamics states that the total entropy of a system either increases or remains constant in any spontaneous process; it never decreases. An important implication of this law is that heat transfers energy spontaneously from higher- to lower-temperature objects, but never spontaneously in the reverse direction.
The second law of thermodynamics is best expressed in terms of a change in the thermodynamic variable known as entropy, which is represented by the symbol S. Entropy, like internal energy, is a state function.
Entropy is the loss of energy available to do work. Another form of the second law of thermodynamics states that the total entropy of a system either increases or remains constant; it never decreases. Entropy is zero in a reversible process; it increases in an irreversible process.
The universe is destined for thermodynamic equilibrium —maximum entropy. This is often called the heat death of the universe, and will mean the end of all activity. Living organisms have evolved to be highly structured, and much lower in entropy than the substances from which they grow.
Entropy, the measure of a system’s thermal energy per unit temperature that is unavailable for doing useful work. Because work is obtained from ordered molecular motion, entropy is also a measure of the molecular disorder, or randomness, of a system.
In classical thermodynamics, entropy (from Greek τρoπή (tropḗ) 'transformation') is a property of a thermodynamic system that expresses the direction or outcome of spontaneous changes in the system.
Entropy (S) is a thermodynamic property of all substances. The greater the number of possible microstates for a system, the greater the disorder and the higher the entropy. Experiments show that the magnitude of ΔS vap is 80–90 J/(mol•K) for a wide variety of liquids with different boiling points.
Thermodynamics - Entropy, Heat, Energy: The concept of entropy was first introduced in 1850 by Clausius as a precise mathematical way of testing whether the second law of thermodynamics is violated by a particular process.