Activity

Name:
Activity
Detailed information:
(1) Chemical activity (thermodynamic activity): a quantity replacing actual molar concentration in mathematical expressions for the equilibrium constant so as to eliminate the effect of concentration on equilibrium constant. (2) Activity coefficient: a fractional number which when multiplied by the molar concentration of a substance in solution yields the chemical activity. This term gives an idea of how much interaction exists between molecules at higher concentration. (3) Activity of metals or elements: an active element will react with a compound of a less active element to produce the latter as the free element, and the active element ends up in a new compound. Thus, magnesium, an active metal, will displace copper from copper sulfate to form magnesium sulfate and free metallic copper; chlorine will liberate iodine from sodium iodide and sodium chloride is formed. See electromotive series. (4) Activity product: the number resulting from the multiplication of the activities of slightly soluble substances. This is frequently called the solubility product. (5) Catalytic activity: see Catalysis. (6) Optical activity: the existence of optical rotation in a substance. (7) Radioactivity activity coefficient. (8) Biology: The true thermodynamic activity of a substance, as distinct from its molar concentration. Most of the time we call the activity equal to the molar concentration and ignore it.See Activity Series (2).