activity coefficient


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ac·tiv·i·ty (a),

(ak-tiv'i-tē),
1. electroencephalography The presence of neurogenic electrical energy.
See also: radioactivity.
2. physical chemistry an ideal concentration for which the law of mass action will apply perfectly; the ratio of the activity to the true concentration is the activity coefficient (γ), which becomes 1.00 at infinite dilution.
See also: radioactivity.
3. For enzymes, the amount of substrate consumed (or product formed) in a given time under given conditions; turnover number.
See also: radioactivity.
4. The number of nuclear transformations (disintegrations) in a given quantity of a material per unit time. Units: curie (Ci), millicurie (mCi), becquerel (Bq), megabecquerel (MBq).
See also: radioactivity.

Activity Coefficient

An idealised concentration of a solute at which the law of mass action acts in a “perfect” fashion, which can be used to determine the solute’s thermodynamic activity.

activity coefficient

1. A factor used in potentiometry to describe the activity of free ions in solution.
2. A vitamin deficiency factor that describes the enhancement of enzyme activity after saturation with a vitamin.
See also: coefficient
References in periodicals archive ?
As a consequence, the sorption parameters and the solvent activity coefficients and the Flory Huggins parameters were calculated only in the temperature range from 60 to 80[degrees]C and for polar-type and dispersion-type solvents in whose retention diagrams this decreasing linear zone can be clearly observed.
Activity coefficients of all species are assumed to be independent of pressure.
The activity coefficients and other thermodynamic properties of hydrochloric acid are dependent not upon the value of E[degrees] but on the difference E-E[degrees].
where [(g.sup.GT.sub.K] and [N.sup.GT.sub.Ca] are the respective adsorbed activity coefficients of the K and Ca ions; [N.sub.K] and [N.sub.Ca] are the respective equivalent fractions of [K.sup.+] and [Ca.sup.2+] on the exchanger; [[gamma].sub.K] and [[gamma].sub.Ca] are the activity coefficients of [K.sup.+] and [Ca.sup.2+] in the equilibrium solution; and [M.sub.K] and [M.sub.Ca] are the [K.sup.+] and [Ca.sup.2+] molarities in the equilibrium solution.
The apparent suppression of Na/K data obtained with ion-selective electrodes is due to junction potential and activity coefficient effect, not to bicarbonate binding [Letter], and Coleman RL, Young CC [Reply].
By obtaining the weight fraction activity coefficient, 1, the partial molar free energy, DG1 , and the average partial molar enthalpy, DH1 values can be calculated from following relations, respectively at infinite dilution [31-33].
Deviation from ideality is accommodated by modifying the activity coefficient. Mass balance equations are solved under the constraint of Raoult's law to determine the extent to which MF evaporates.
General results are based on ([partial derivative][g.sup.E]/[[partial derivative][x.sub.1]).sub.az] = R[T.sub.az] In[[p.sub.2.sup.*]([T.sub.az])/[p.sub.1.sup.*]([T.sub.az])], and [P.sub.az] = [([gamma].sub.1][p.sub.1.sup.*]).sub.az] = [([gamma].sub.2][p.sub.2.sup.*]).sub.az], where R is the gas constant, [p.sub.*] is saturation vapour pressure, and [gamma] is liquid-phase activity coefficient. Specific results are given for the Redlich-Kister, van Laar, Wilson, and NRTL equations.
where m is the equilibrium concentrations (mol/L), [gamma]N[H.sub.4] is the single ion activity coefficient for N[H.sub.4.sup.+], and [gamma]Ca is the single ion activity coefficient for [Ca.sup.2+].