QRxn

qrxn is a term encountered in chemistry and computational chemistry that can refer to more than one concept. There is no single canonical definition; usage depends on context.

In chemical thermodynamics and kinetics, qrxn (often written as Qrxn or Q_rxn) denotes the reaction quotient. For a reaction aA + bB ⇌ cC + dD, Qrxn is the ratio of the activities (or concentrations) of products raised to their stoichiometric coefficients to the activities of reactants raised to their coefficients. At a given temperature, Qrxn is compared with the equilibrium constant K to assess the direction of spontaneous change: Qrxn < K favors the forward (product-forming) direction, while Qrxn > K favors the reverse direction.

In software and data science, qrxn is used as the name or acronym for tools, libraries, or projects that model chemical reaction networks. Such tools typically allow users to define reactions by stoichiometry and rate laws, assemble the network, and simulate its time evolution using deterministic solvers for ordinary differential equations or stochastic methods such as the Gillespie algorithm. They may support standard data formats, enable parameter estimation and sensitivity analysis, and provide visualization of reaction fluxes and state trajectories.

Etymology and usage vary, with different spellings and capitalizations (qrxn, Qrxn, QRxn) across sources. In practice, the term is context-dependent and is not tied to a single organization or project.