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Zeroth law of thermodynamics. The zeroth law of thermodynamics states that if two separate thermodynamic systems are each in thermal equilibrium with a third, then all three are in thermal equilibrium with each other.

Zeroth law of thermodynamics

Two systems are said to be in the relation of thermal equilibrium if they are linked by a wall permeable only to heat, and do not change over time.[1] As a convenience of language, systems are sometimes also said to be in a relation of thermal equilibrium if they are not linked so as to be able to transfer heat to each other, but would not do so if they were connected by a wall permeable only to heat. Viscosity. Etymology[edit] The word "viscosity" is derived from the Latin "viscum", meaning "anything sticky, birdlime made from mistletoe, mistletoe".


A viscous glue called birdlime was made from mistletoe berries and was used for lime-twigs to catch birds.[2] Definition[edit] Dynamic (shear) viscosity[edit] Laminar shear of fluid between two plates. Third law of thermodynamics. The third law of thermodynamics is sometimes stated as follows, regarding the properties of systems in equilibrium at absolute zero temperature: The entropy of a perfect crystal, at absolute zero kelvin, is exactly equal to zero.

Third law of thermodynamics

The Nernst-Simon statement of the third law of thermodynamics is in regard to thermodynamic processes, and whether it is possible to achieve absolute zero in practice: The entropy change associated with any condensed system undergoing a reversible isothermal process approaches zero as temperature approaches 0 K, where condensed system refers to liquids and solids. Thermodynamic system. A thermodynamic system is a precisely specified macroscopic region of the universe, defined by boundaries or walls of particular natures, together with the physical surroundings of that region, which determine processes that are allowed to affect the interior of the region, studied using the principles of thermodynamics.

Thermodynamic system

Thermodynamic state. Thermodynamic process. A thermodynamic process is the energetic development of a thermodynamic system proceeding from an initial state to a final state.

Thermodynamic process

Paths through the space of thermodynamic variables are often specified by holding certain thermodynamic variables constant. A state function is a thermodynamic variable which depends only on the current state of the system, not the path taken to reach that state. Conversely a process function does depend on the path. Overview[edit] Thermodynamic potential. Description and interpretation[edit] Five common thermodynamic potentials are:[1] These five common potentials are all energy potentials, but there are also entropy potentials.

Thermodynamic potential

Thermodynamic equilibrium. In thermodynamics, a thermodynamic system is in thermodynamic equilibrium when it is in thermal equilibrium, mechanical equilibrium, radiative equilibrium, and chemical equilibrium.

Thermodynamic equilibrium

Equilibrium means a state of balance. In a state of thermodynamic equilibrium, there are no net flows of matter or of energy, no phase changes, and no unbalanced potentials (or driving forces), within the system. A system that is in thermodynamic equilibrium experiences no changes when it is isolated from its surroundings. In non-equilibrium systems there are net flows of matter or energy, or phase changes are occurring; if such changes can be triggered to occur in a system in which they are not already occurring, it is said to be in a metastable equilibrium.

Temperature. A map of global long term monthly average surface air temperatures in Mollweide projection.


Statistical ensemble (mathematical physics) In mathematical physics, especially as introduced into statistical mechanics and thermodynamics by J.

Statistical ensemble (mathematical physics)

State function. In contrast, mechanical work and heat are process quantities because their values depend on the specific transition (or path) between two equilibrium states.

State function

History[edit] It is likely that the term “functions of state” was used in a loose sense during the 1850s and 60s by those such as Rudolf Clausius, William Rankine, Peter Tait, William Thomson, and it is clear that by the 1870s the term had acquired a use of its own. In 1873, for example, Willard Gibbs, in his paper “Graphical Methods in the Thermodynamics of Fluids”, states: “The quantities V, B, T, U, and S are determined when the state of the body is given, and it may be permitted to call them functions of the state of the body.” Overview[edit] ). ). Spontaneous process. A spontaneous process is the time-evolution of a system in which it releases free energy (usually as heat) and moves to a lower, more thermodynamically stable energy state.[1][2] The sign convention of changes in free energy follows the general convention for thermodynamic measurements, in which a release of free energy from the system corresponds to a negative change in free energy, but a positive change for the surroundings.

Depending on the nature of the process, the free energy is determined differently. For example, the Gibbs free energy is used when considering processes that occur under constant pressure and temperature conditions whereas the Helmholtz free energy is used when considering processes that occur under constant volume and temperature conditions. A spontaneous process is capable of proceeding in a given direction, as written or described, without needing to be driven by an outside source of energy.

Overview[edit] Second law of thermodynamics. The second law of thermodynamics states that the entropy of an isolated system never decreases, because isolated systems always evolve toward thermodynamic equilibrium, a state with maximum entropy. The second law refers to increases in entropy that can be analyzed into two varieties, due to dissipation of energy and due to dispersion of matter. One may consider a compound thermodynamic system that initially has interior walls that restrict transfers within it.

The second law refers to events over time after a thermodynamic operation on the system, that allows internal heat transfers, removes or weakens the constraints imposed by its interior walls, and isolates it from the surroundings. Reversible process (thermodynamics) In thermodynamics, a reversible process -- or reversible cycle if the process is cyclic -- is a process that can be "reversed" by means of infinitesimal changes in some property of the system without entropy production (i.e. dissipation of energy).[1] Due to these infinitesimal changes, the system is in thermodynamic equilibrium throughout the entire process.

Since it would take an infinite amount of time for the reversible process to finish, perfectly reversible processes are impossible. However, if the system undergoing the changes responds much faster than the applied change, the deviation from reversibility may be negligible. In a reversible cycle, the system and its surroundings will be exactly the same after each cycle.[2] In thermodynamics, processes can be carried out in one of two ways: reversibly or irreversibly. Reversibility in thermodynamics refers to performing a reaction continuously at equilibrium. Pressure. Pressure as exerted by particle collisions inside a closed container. Pressure (symbol: p or P) is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled gage pressure)[a][not in citation given] is the pressure relative to the local atmospheric or ambient pressure.

Definition[edit] Pressure is the amount of force acting per unit area. Partition function (statistical mechanics) The canonical partition function is where the "inverse temperature", β, is conventionally defined as with kB denoting Boltzmann's constant. The exponential factor exp(−βEs) is known as the Boltzmann factor. Non-equilibrium thermodynamics. Non-equilibrium thermodynamics is a branch of thermodynamics that deals with thermodynamic systems that are not in thermodynamic equilibrium.

Most systems found in nature are not in thermodynamic equilibrium; for they are changing or can be triggered to change over time, and are continuously and discontinuously subject to flux of matter and energy to and from other systems and to chemical reactions. Non-equilibrium thermodynamics is concerned with transport processes and with the rates of chemical reactions.[1] Many natural systems still today remain beyond the scope of currently known macroscopic thermodynamic methods. The thermodynamic study of non-equilibrium systems requires more general concepts than are dealt with by equilibrium thermodynamics.

Internal energy. For practical considerations in thermodynamics and engineering it is rarely necessary or convenient to consider all energies belonging to the total intrinsic energy of a sample system, such as the energy given by the equivalence of mass. Typically, descriptions only include components relevant to the system under study. Ideal gas law. Heat. In physics, heating is transfer of energy from a hotter body to a colder one, other than by work or transfer of matter. It occurs spontaneously whenever a suitable physical pathway exists between the bodies.[1][2][3][4][5][6] The pathway can be direct, as in conduction and radiation, or indirect, as in convective circulation.[7][8][9] Heating is a dissipative process.

Thermodynamic free energy. First law of thermodynamics. History. Equipartition theorem. Thermal motion of an α-helicalpeptide. The jittery motion is random and complex, and the energy of any particular atom can fluctuate wildly. Equation of state. Overview[edit] The most prominent use of an equation of state is to correlate densities of gases and liquids to temperatures and pressures. One of the simplest equations of state for this purpose is the ideal gas law, which is roughly accurate for weakly polar gases at low pressures and moderate temperatures. However, this equation becomes increasingly inaccurate at higher pressures and lower temperatures, and fails to predict condensation from a gas to a liquid. Therefore, a number of more accurate equations of state have been developed for gases and liquids. Entropy. Enthalpy. Conjugate variables (thermodynamics) Boltzmann constant.