Thermodynamic States & Processes

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Abstractions about thermodynamic systems and their transformations, including state and process functions (Gibbs free energy, enthalpy, entropy), classifications of processes as spontaneous, exothermic or exergonic, phase-equilibrium relations (freezing-point depression, Duhem-Margules), and heat- or mass-transfer diagrams and methods.

31 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.
• 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.
• 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.
• Exothermic process — A thermodynamic process that transfers energy from the system to its surroundings as heat under a declared boundary and sign convention.
• Eötvös rule — An empirical corresponding-states relation approximating how a pure liquid’s surface tension decreases toward zero near its critical temperature.
• Fractional crystallization (chemistry) — A staged separation in which components crystallize preferentially as temperature or composition changes, allowing purified solid fractions to be removed from a multicomponent liquid.
• 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.
• Gibbs free energy — A thermodynamic potential equal to enthalpy minus temperature times entropy that governs equilibrium and non-expansion work at fixed temperature and pressure.
• Heat release parameter — A dimensionless combustion parameter comparing adiabatic temperature rise with unburned-mixture temperature.
• Joule expansion — An irreversible free expansion in which a gas initially confined in an insulated rigid vessel expands into an evacuated region after a partition is removed.
• Mass transfer — Net transport of a chemical species or material component between locations, phases, or streams by diffusion, convection, and interfacial exchange.
• Negative thermal expansion — The material response in which length or volume decreases over a temperature interval as temperature increases.
• NTU method — A heat-exchanger analysis method that combines effectiveness, heat-capacity rates and number of transfer units to determine heat transfer when outlet temperatures are unknown.
• Pressure–volume diagram — A plot of system pressure against volume along one or more processes, whose path shape represents state change and whose enclosed or signed area represents boundary work.
• 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.
• Process function — A thermodynamic quantity such as heat or work whose value depends on the path connecting equilibrium states rather than on the endpoints alone.
• 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.
• Scale of temperature — A calibrated mapping from thermometric states to ordered numerical temperature values under a declared reference and unit.
• Simon–Glatzel equation — An empirical power-law correlation relating a solid’s melting temperature to pressure through fitted reference pressure and exponent parameters.
• Spontaneous process — A thermodynamic change that proceeds in its favored direction without continuous external driving because the relevant free energy decreases under stated constraints.
• 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.
• State function — A thermodynamic property determined only by the system’s equilibrium state, so its change is independent of the path between two states.
• Temperature–entropy diagram — A thermodynamic plot of temperature against specific entropy used to visualize processes and cycles, with reversible heat transfer represented by area under the path.
• Thermodynamic process — A transformation carrying a thermodynamic system between states through a specified path of heat, work and matter exchange.
• 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.