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In thermodynamics, a change in the thermodynamic state of a system and all of its surroundings cannot be precisely restored to its initial state by infinitesimal changes in some property of the system without expenditure of energy. A system that undergoes an irreversible process may still be capable of returning to its initial state.
In physics, chemistry, and other related fields like biology, a phase transition (or phase change) is the physical process of transition between one state of a medium and another. Commonly the term is used to refer to changes among the basic states of matter: solid, liquid, and gas, and in rare cases, plasma.
For thermodynamics, a natural process is a transfer between systems that increases the sum of their entropies, and is irreversible. [2] Natural processes may occur spontaneously upon the removal of a constraint, or upon some other thermodynamic operation , or may be triggered in a metastable or unstable system, as for example in the ...
Figure 1. A thermodynamic model system. Differences in pressure, density, and temperature of a thermodynamic system tend to equalize over time. For example, in a room containing a glass of melting ice, the difference in temperature between the warm room and the cold glass of ice and water is equalized by energy flowing as heat from the room to the cooler ice and water mixture.
When matter is transferred into a system, the internal energy and potential energy associated with it are transferred into the new combined system. ( u Δ M ) i n = Δ U s y s t e m {\displaystyle \left(u\,\Delta M\right)_{\rm {in}}=\Delta U_{\rm {system}}} where u denotes the internal energy per unit mass of the transferred matter, as measured ...
For a similar process at constant temperature and volume, the change in Helmholtz free energy must be negative, <. Thus, a negative value of the change in free energy (G or A) is a necessary condition for a process to be spontaneous. This is the most useful form of the second law of thermodynamics in chemistry, where free-energy changes can be ...
Why does 1.5C matter and how will future climate change affect the world? ... changes could accelerate and become irreversible, such as the collapse of the Greenland Ice Sheet.
Many physical changes also involve the rearrangement of atoms most noticeably in the formation of crystals. Many chemical changes are irreversible, and many physical changes are reversible, but reversibility is not a certain criterion for classification. Although chemical changes may be recognized by an indication such as odor, color change, or ...