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Enthalpy of fusion
The enthalpy of fusion, also called the latent heat of fusion, is the heat needed to melt a substance at constant pressure. For water it is 334 kJ/kg.
Enthalpy of solution
The enthalpy of solution is the heat absorbed or released when a solute dissolves in a solvent at constant temperature and pressure; ammonium nitrate dissolving cools a cold pack, while calcium chloride warms a hot pack.
Enthalpy of sublimation
The enthalpy of sublimation, ΔsubH, is the heat required to convert one mole of solid directly to gas, and it always exceeds the enthalpy of vaporization.
Enthalpy of vaporization (ΔvapH)
The enthalpy of vaporization, or latent heat of vaporization, is the heat needed to turn a liquid into gas, about 40.7 kJ/mol for water at 100 °C.
Entire function
An entire function, also called an integral function, is a complex-valued function that is complex differentiable everywhere on the complex plane; polynomials, the exponential, sine, and cosine are entire.
Entisols
Entisols are one of the 12 orders of USDA Soil Taxonomy: mineral soils with little or no horizon development, covering about 18 percent of Earth's ice-free land.
Entity realism
Entity realism is a position in the philosophy of science, coined by Ian Hacking, holding that belief in unobservable entities like electrons is justified by experimental manipulation, without trusting theories.
Entrainment (hydrodynamics)
Entrainment in hydrodynamics is the incorporation of surrounding ambient fluid across the boundary of a turbulent jet, plume, or density current, quantified by an entrainment coefficient α.
Entrance length
Entrance length, also called hydrodynamic entry length or development length, is the distance a fluid travels after entering a pipe before its velocity profile stops changing and becomes fully developed.
Entrance pupil
The entrance pupil, also called the no-parallax point, is the image of a lens's aperture stop seen from object space, and it fixes the lens's f-number.
Entropic bonding
Entropic bonding is the bond-like attraction between hard particles such as nanoparticles or colloids that arises purely from entropy, since certain arrangements free space for neighbors.
Entropic force
An entropic force is an effective macroscopic force arising from statistical rearrangements that drive a system toward greater entropy, seen in polymer elasticity, depletion forces, and osmotic pressure.
Entropic gravity
Entropic gravity, or gravity as an entropic force, is Erik Verlinde's 2010 hypothesis that gravity emerges thermodynamically from changes in information, extended in 2016 to explain dark matter.
Entropic uncertainty relations
An entropic uncertainty relation is a lower bound on the Shannon entropies of outcomes from incompatible quantum measurements, constraining the full spread rather than variances.
Entropy
Entropy, or Entropie, is a thermodynamic quantity measuring the microscopic arrangements consistent with a system's macroscopic condition; Clausius introduced it, and Boltzmann, Gibbs, and Shannon generalized it.
Entropy (information theory)
Entropy, also called Shannon entropy, measures the average uncertainty of a random variable; Claude Shannon introduced it in 1948 as a lower bound on lossless compression.
Entropy (statistical thermodynamics)
Entropy in statistical thermodynamics, also called Boltzmann-Gibbs entropy, measures how many microstates are consistent with a macrostate, expressed as S = k ln W and grounding the second law probabilistically.
Entropy and life
Entropy and life is the study of how living organisms sustain local order by consuming free energy and exporting entropy, resolving their apparent conflict with the second law of thermodynamics.
Entropy as an arrow of time
Entropy as an arrow of time is the thesis that time's direction is fixed by entropy increasing toward the future, grounded in the second law of thermodynamics.
Entropy balancing
Entropy balancing is a reweighting method for causal inference and survey statistics, introduced by Jens Hainmueller in 2012, that reweights controls to match treated-group covariate moments.
Entropy of entanglement
The entropy of entanglement, or entanglement entropy, is a measure of quantum entanglement for a pure bipartite quantum state, defined as the von Neumann entropy of either subsystem's reduced density matrix.
Entropy of mixing
The entropy of mixing, also called Gibbs theorem, is the thermodynamic entropy change on combining pure substances; it is always positive for ideal mixtures and depends only on mole fractions.
Entropy of the universe
The entropy of the universe is the total thermodynamic entropy in the observable universe, estimated at about 10^104 k, with supermassive black holes contributing almost all of it.
Entropy production
Entropy production, also called entropy generation, is the rate at which entropy is created inside a system by irreversible processes, quantifying how far a process sits from thermodynamic equilibrium.
Entropy weight method
The entropy weight method is an objective weighting technique in multi-criteria decision analysis that derives criterion weights from Shannon entropy in the decision matrix, minimizing subjective judgment.
Entropy-stabilized PbTe
Entropy-stabilized PbTe is lead telluride thermoelectric material in which multi-element alloying raises configurational entropy, stabilizing a single-phase rock-salt solid solution and lowering lattice thermal conductivity.
Entscheidungsproblem
The Entscheidungsproblem, also known as Church's theorem, is the problem of deciding validity in first-order logic, posed by Hilbert and Ackermann in 1928 and proved unsolvable by Church and Turing in 1936.
Enumeration
Enumeration is the branch of combinatorics concerned with counting the elements of finite sets, using tools such as generating functions, bijective proofs, and Pólya's theorem for counting under symmetry.
Enumeration algorithm
An enumeration algorithm lists every element of a finite solution set exactly once, without repetition, producing results as a stream that can be consumed as they appear.
Enumeration degree
An enumeration degree is an equivalence class of sets of natural numbers under enumeration reducibility, where one set is computed from positive information about another.