Difference between revisions of "Activity"
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{{MitoPedia | {{MitoPedia | ||
|abbr=''a'' | |abbr=''a'' | ||
|description=The '''activity''' (relative activity) is a dimensionless quantity related to the concentration or partial pressure of dissolved substances. The activity of a dissolved substance B equals the [[concentration]], ''c''<sub>B</sub> [ | |description=The '''activity''' (relative activity) is a dimensionless quantity related to the concentration or partial pressure of dissolved substances. The activity of a dissolved substance B equals the [[concentration]], ''c''<sub>B</sub> [mol·L<sup>-1</sup>] at high dilution divided by the unit concentration, ''c''° = 1 mol·L<sup>-1</sup>: | ||
''a''<sub>B</sub> = ''c''<sub>B</sub>/''c''° | ''a''<sub>B</sub> = ''c''<sub>B</sub>/''c''° | ||
This simple relationship applies frequently to dilutions <10 | This simple relationship applies frequently to dilutions <10 mmol·L<sup>-1</sup> (<10 mol·m<sup>-3</sup>. In general, the concentration of a [[solute]] has to be corrected for the activity coefficient (concentration basis), ''γ''<sub>B</sub>, | ||
''a''<sub>B</sub> = ''γ''<sub>B</sub>·''c''<sub>B</sub>/''c''° | ''a''<sub>B</sub> = ''γ''<sub>B</sub>·''c''<sub>B</sub>/''c''° | ||
At high dilution, ''γ''<sub>B</sub> = 1. | At high dilution, ''γ''<sub>B</sub> = 1. | ||
For a dissolved gas G, the activity is the partial pressure, ''p''<sub>G</sub> [Pa], divided by the unit partial pressure, ''p''° = 1 Pa. The partial pressure is related to the concentration of the gas by the [[solubility]], ''S''<sub>G</sub> [Pa/mol] (''see'' [[Oxygen solubility]]): | For a dissolved gas G, the activity is the partial pressure, ''p''<sub>G</sub> [Pa] (strictly: fugacity), divided by the unit partial pressure, ''p''° = 1 Pa. The partial pressure is related to the concentration of the gas by the [[solubility]], ''S''<sub>G</sub> [Pa/mol] (''see'' [[Oxygen solubility]]): | ||
''a''<sub>G</sub> = ''c''<sub>G</sub>·''S''<sub>G</sub>/''p''° | ''a''<sub>G</sub> = ''c''<sub>G</sub>·''S''<sub>G</sub>/''p''° | ||
In general, the relative activity is defined by the chemical potential, ''µ''<sub>X</sub> | In general, the relative activity is defined by the chemical potential, ''µ''<sub>X</sub> | ||
Revision as of 08:48, 20 October 2018
- high-resolution terminology - matching measurements at high-resolution
Activity
Description
The activity (relative activity) is a dimensionless quantity related to the concentration or partial pressure of dissolved substances. The activity of a dissolved substance B equals the concentration, cB [mol·L-1] at high dilution divided by the unit concentration, c° = 1 mol·L-1:
aB = cB/c°
This simple relationship applies frequently to dilutions <10 mmol·L-1 (<10 mol·m-3. In general, the concentration of a solute has to be corrected for the activity coefficient (concentration basis), γB,
aB = γB·cB/c°
At high dilution, γB = 1.
For a dissolved gas G, the activity is the partial pressure, pG [Pa] (strictly: fugacity), divided by the unit partial pressure, p° = 1 Pa. The partial pressure is related to the concentration of the gas by the solubility, SG [Pa/mol] (see Oxygen solubility):
aG = cG·SG/p°
In general, the relative activity is defined by the chemical potential, µX
aX = exp[(µX-µ°)/RT]
Abbreviation: a
Reference: Cohen 2008 IUPAC Green Book
Communicated by Gnaiger E 2018-10-18
Activity in other contexts
- Free activity
- Activity of a radioactive substance, A = — dNB/dt [Bq] [1]
- Bq is the becquerel [s-1]
References
- ↑ Cohen ER, Cvitas T, Frey JG, Holmström B, Kuchitsu K, Marquardt R, Mills I, Pavese F, Quack M, Stohner J, Strauss HL, Takami M, Thor HL (2008) Quantities, Units and Symbols in Physical Chemistry, IUPAC Green Book, 3rd Edition, 2nd Printing, IUPAC & RSC Publishing, Cambridge. - »Bioblast link«
MitoPedia concepts:
Ergodynamics
MitoPedia topics:
Substrate and metabolite
