Back حاصل قسمة التفاعل Arabic Quocient de reacció Catalan Reaktionsquotient German Cociente de reacción Spanish بهره واکنش FA Reaktio-osamäärä Finnish Reactiequotiënt Dutch Reaksjonskvotient NB Reaktionskvot Swedish 反应商 Chinese
In chemical thermodynamics, the reaction quotient (Qr or just Q)[1] is a dimensionless quantity that provides a measurement of the relative amounts of products and reactants present in a reaction mixture for a reaction with well-defined overall stoichiometry at a particular point in time. Mathematically, it is defined as the ratio of the activities (or molar concentrations) of the product species over those of the reactant species involved in the chemical reaction, taking stoichiometric coefficients of the reaction into account as exponents of the concentrations. In equilibrium, the reaction quotient is constant over time and is equal to the equilibrium constant.
A general chemical reaction in which α moles of a reactant A and β moles of a reactant B react to give ρ moles of a product R and σ moles of a product S can be written as
- .
The reaction is written as an equilibrium even though, in many cases, it may appear that all of the reactants on one side have been converted to the other side. When any initial mixture of A, B, R, and S is made, and the reaction is allowed to proceed (either in the forward or reverse direction), the reaction quotient Qr, as a function of time t, is defined as[2]
where {X}t denotes the instantaneous activity[3] of a species X at time t. A compact general definition is
![{\displaystyle Q_{\text{r}}(t)=\prod _{j}[a_{j}(t)]^{\nu _{j}},}](https://wikimedia.org/api/rest_v1/media/math/render/svg/96769e0073977fe81ed041888f0b5cabc8a50366)
where Пj denotes the product across all j-indexed variables, aj(t) is the activity of species j at time t, and νj is the stoichiometric number (the stoichiometric coefficient multiplied by +1 for products and –1 for starting materials).
- ^ Cohen, E Richard; Cvitas, Tom; Frey, Jeremy G; Holström, Bertil; Kuchitsu, Kozo; Marquardt, Roberto; Mills, Ian; Pavese, Franco; Quack, Martin, eds. (2007). Quantities, Units and Symbols in Physical Chemistry (3 ed.). Cambridge: Royal Society of Chemistry. doi:10.1039/9781847557889. ISBN 978-0-85404-433-7.
- ^ Zumdahl, Steven; Zumdahl, Susan (2003). Chemistry (6th ed.). Houghton Mifflin. ISBN 0-618-22158-1.
- ^ Under certain circumstances (see chemical equilibrium) each activity term such as {A} may be replaced by a concentration term, [A]. Both the reaction quotient and the equilibrium constant are then concentration quotients.