Equivalent (chemistry)

Equivalent (chemistry)

The equivalent (symbol: eq or Eq), sometimes termed the molar equivalent, is a unit of amount of substance used in chemistry and the biological sciences.

The equivalent is formally defined as the amount of a substance which will either:

The mass of one equivalent of a substance is called its equivalent weight.

A historical definition, used especially for the chemical elements, describes an equivalent as the amount of a substance that will react with one gram of hydrogen, or with sixteen grams of oxygen or with 35.5 grams (1.25 oz) of chlorine or displaces any of the three.[3]

In practice, the amount of a substance in equivalents often has a very small magnitude, so it is frequently described in terms of milliequivalents (mEq or meq), the prefix milli denoting that the measure is divided by 1000. Very often, the measure is used in terms of milliequivalents of solute per litre of solvent (or milliNormal, where mEq/l = mN). This is especially common for measurement of compounds in biological fluids; for instance, the healthy level of potassium in the blood of a human is defined between 3.5 and 5.0 mEq/l.

Use in biochemistry and medicine

The composition of drug preparations, such as intravenous fluids, is often stated in mmol/l rather than mEq/l. The molarity refers to the number of dissolved particles, and does not account for the number of available charges. For that reason, for an element such as Na+, which has a valence of 1, 1 mmol/l = 1 mEq/l, whereas for a divalent element (i.e. an element having a valence of 2) such as Mg2+ or Ca2+, 1 mmol/l = 2 mEq/l.


  1. ^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version:  (2006–) "equivalent entity".
  2. ^ International Union of Pure and Applied Chemistry (1998). Compendium of Analytical Nomenclature (definitive rules 1997, 3rd. ed.). Oxford: Blackwell Science. ISBN 0-86542-6155. section 6.3.
  3. ^ "Atome", Grand dictionnaire universel du XIXe siècle, 1, Paris: Pierre Larousse, 1866, pp. 868–73 . (French)

External links

Wikimedia Foundation. 2010.

Игры ⚽ Поможем сделать НИР

Look at other dictionaries:

  • Chemistry: A Volatile History — is a 2010 BBC documentary on the history of chemistry presented by Jim Al Khalili. It was nominated for the 2010 British Academy Television Awards in the category Specialist Factual. Contents 1 Episode 1 – Discovering the Elements 1.1… …   Wikipedia

  • Equivalent weight — is the amount of an element that reacts, or is involved in reaction with, 1 mole of electrons. It is defined by many texts as the weight of the element combining with 1 g hydrogen, 8 g oxygen or 35.5 g chlorine, each of which would either provide …   Wikipedia

  • chemistry — /kem euh stree/, n., pl. chemistries. 1. the science that deals with the composition and properties of substances and various elementary forms of matter. Cf. element (def. 2). 2. chemical properties, reactions, phenomena, etc.: the chemistry of… …   Universalium

  • equivalent weight — Chem. the combining power, esp. in grams (gram equivalent), of an element or compound, equivalent to hydrogen as a standard of 1.00797 or oxygen as a standard of 8; the atomic weight divided by the valence. [1925 30] * * * or combining weight… …   Universalium

  • Chemistry (etymology) — In the history of science, the etymology of the word chemistry is a debatable issue. It is agreed that the word derives from the word alchemy, which is a European one, derived from the Arabic al kīmīā (الكيمياء). The Arabic term is derived from… …   Wikipedia

  • equivalent weight — noun the atomic weight of an element that has the same combining capacity as a given weight of another element; the standard is 8 for oxygen • Syn: ↑equivalent, ↑combining weight, ↑eq • Hypernyms: ↑atomic mass, ↑atomic weight, ↑relative atomic… …   Useful english dictionary

  • equivalent — [ɪ kwɪv(ə)l(ə)nt] adjective 1》 equal in value, amount, function, meaning, etc.     ↘(equivalent to) having the same or a similar effect as. 2》 Mathematics belonging to the same equivalence class. noun 1》 a person or thing that is equivalent to… …   English new terms dictionary

  • equivalent — e quiv·a·lent || nt n. something equivalent, something equal in value or importance; equivalent proportion (Chemistry) adj. equal in worth or value, equal in importance; corresponding …   English contemporary dictionary

  • equivalent —    or equivalent weight (Eq)    a unit of relative amount of substance used in chemistry. One equivalent weight of an element, compound, or ion is the weight in grams of that substance which would react with or replace one gram of hydrogen. Since …   Dictionary of units of measurement

  • equivalent — /əˈkwɪvələnt / (say uh kwivuhluhnt), /i / (say ee ) adjective 1. equal in value, measure, force, effect, significance, etc. 2. corresponding in position, function, etc. 3. Chemistry having the same capacity to combine or react chemically. –noun 4 …  

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”