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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.
- 19.2: Entropy and the Second Law of Thermodynamics
As an example of an irreversible process, consider the...
- 18.4: Entropy Changes Associated with State Changes
In this system, some heat (δQ) from the warmer surroundings...
- 4.7: Entropy - Physics LibreTexts
Example \(\PageIndex{1}\): Entropy Change of Melting Ice....
- 19.2: Entropy and the Second Law of Thermodynamics
Define entropy and calculate the increase of entropy in a system with reversible and irreversible processes. Explain the expected fate of the universe in entropic terms. Calculate the increasing disorder of a system. Figure 15.31 The ice in this drink is slowly melting.
As an example of an irreversible process, consider the entropy changes that accompany the spontaneous and irreversible transfer of heat from a hot object to a cold one, as occurs when lava spewed from a volcano flows into cold ocean water.
In this system, some heat (δQ) from the warmer surroundings at 298 K (25 °C; 77 °F) transfers to the cooler system of ice and water at its constant temperature (T) of 273 K (0 °C; 32 °F), the melting temperature of ice. The entropy of the system, which is δQ/T, increases by δQ/273K.
Example \(\PageIndex{1}\): Entropy Change of Melting Ice. Heat is slowly added to a 50-g chunk of ice at \(0^oC\) until it completely melts into water at the same temperature. What is the entropy change of the ice? Strategy. Because the process is slow, we can approximate it as a reversible process.
Entropy is related not only to the unavailability of energy to do work; it is also a measure of disorder. For example, in the case of a melting block of ice, a highly structured and orderly system of water molecules changes into a disorderly liquid, in which molecules have no fixed positions (Figure 12.11). There is a large increase in entropy ...
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.
