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Specific entropy may be expressed relative to a unit of mass, typically the kilogram (unit: J⋅kg −1 ⋅K −1 ). Alternatively, in chemistry, it is also referred to one mole of substance, in which case it is called the molar entropy with a unit of J⋅mol −1 ⋅K −1 .
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.
Jul 31, 2024 · 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.
Entropy, like internal energy, is a state function. This means that when a system makes a transition from one state into another, the change in entropy \(\Delta S\) is independent of path and depends only on the thermodynamic variables of the two states.
Entropy behaves in predictable ways. In Physics the basic definition is: S = k B log(Ω) Where: S is entropy; k B is Boltzmann's Constant (1.380649×10 −23 J/K) Ω is the number of "Microstates" Another important formula is: ΔS = QT. Where: ΔS is the change in entropy; Q is the flow of heat energy in or out of the system; T is temperature
Changes in entropy (ΔS), together with changes in enthalpy (ΔH), enable us to predict in which direction a chemical or physical change will occur spontaneously. Before discussing how to do so, however, we must understand the difference between a reversible process and an irreversible one.
Nov 28, 2021 · In physical chemistry and thermodynamics, one useful entropy formula relates entropy to the internal energy (U) of a system: dU = T dS – p dV. Here, the change in internal energy dU equals absolute temperature T multiplied by the change in entropy minus external pressure p and the change in volume V.
