Physical Chemistry & Phase Relations

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Abstractions about thermodynamic and molecular relations governing phases, reactions, transport, and equilibrium. They include activity and state equations, mass transfer, evaporation, reaction enthalpy, electrochemical diagrams, intermolecular potentials, critical variables, and minimum-energy principles.

25 abstractions in this family — domain-specific abstractions that sit near one another in structural-signature space (k-means over structural-signature embeddings). Each is shown with its short description.

• Bodenstein number — A dimensionless transport ratio comparing convective throughput with axial diffusion or dispersion in a flowing reactor or conduit.
• Charge number — The dimensionless electric charge of a particle, ion or system expressed as a signed multiple of the elementary charge, z=q/e.
• Compressed fluid — A liquid-state fluid at a pressure above its saturation pressure for the given temperature, equivalently below saturation temperature at the given pressure, and therefore not about to vaporize under that condition.
• Control coefficient (biochemistry) — A metabolic-control coefficient measuring the fractional sensitivity of steady-state flux or concentration to a fractional change in one system component.
• Critical variable — A thermodynamic state variable evaluated at a fluid's critical point, such as critical temperature, pressure or molar volume, where liquid and vapor phases become indistinguishable.
• Davies equation — An empirical extension of Debye–Hückel theory that estimates electrolyte activity coefficients from ionic strength by adding a fitted finite-concentration correction.
• Duhem–Margules equation — A binary-mixture thermodynamic constraint equating composition-scaled changes in the components’ equilibrium partial vapor pressures.
• Evaporation — Surface vaporization in which molecules escape from a liquid into the gas phase, with net rate governed by temperature, vapor pressure, ambient concentration, flow and available surface.
• Exergonic process — A process whose Gibbs free-energy change is negative under declared temperature, pressure, composition, and state conventions, making the forward change thermodynamically favorable.
• Eötvös rule — An empirical corresponding-states relation approximating how a pure liquid’s surface tension decreases toward zero near its critical temperature.
• Freezing-point depression — The lowering of a solvent’s equilibrium freezing temperature caused by dissolved solute or mixing with another component.
• Gas separation — Partition a gas mixture into enriched or purified streams by exploiting differential volatility, adsorption, membrane permeability, absorption, chemical affinity, or kinetic response under a specified product and energy objective.
• Mass transfer — Net transport of a chemical species or material component between locations, phases, or streams by diffusion, convection, and interfacial exchange.
• Mie potential — A two-power pair potential combining short-range repulsion and longer-range attraction between particles.
• Molar refractivity — A molar optical-response quantity combining refractive index and density to estimate the electronic polarizability contributed by one mole of material.
• Molecularity — The number of reacting species participating in one elementary reaction step as written in its molecular mechanism.
• Pourbaix diagram — A potential-versus-pH phase map showing thermodynamically predominant aqueous species and solid phases for a declared electrochemical system.
• Principle of minimum energy — A thermodynamic equilibrium principle stating that at fixed entropy and external parameters, a closed system's internal energy is minimized among nearby admissible states.
• Residual property (physics) — A thermodynamic departure function equal to a real-fluid property minus the corresponding ideal-gas property at the same temperature, density or volume, and composition.
• Simon–Glatzel equation — An empirical power-law correlation relating a solid’s melting temperature to pressure through fitted reference pressure and exponent parameters.
• Standard enthalpy of reaction — The enthalpy change for a reaction as written when reactants and products occupy their specified standard states at a stated temperature.
• Standard state — A specified thermodynamic reference condition for a substance at a chosen standard pressure and composition convention, used to define activities and tabulate standard-state properties.
• Thermoneutral voltage — The electrochemical-cell voltage whose electrical energy per unit charge equals the reaction enthalpy, so ideal operation needs no net external heat to remain isothermal.
• Transition state — The highest-free-energy configuration along a chosen reaction path, defining the dividing surface between reactants and products and controlling reaction-rate theory.
• UNIQUAC — A local-composition activity-coefficient model that splits a liquid mixture's excess Gibbs energy into combinatorial size-shape and residual interaction terms.