Everything about The Amount Of Substance totally explained
The
amount of substance,
n, of a sample or system is a
physical quantity which is
proportional to the number of
elementary entities present. "Elementary entities" may be atoms, molecules, ions, electrons, or particles, the choice of which is dependent upon context and must be stated. Amount of substance is sometimes referred to as
chemical amount or, incorrectly, as
number of moles.
The
SI unit for amount of substance is the
mole (mol), which is defined as the amount of substance that has an equal number of elementary entities as there are atoms in 12
g of
carbon-12. That number is the
Avogadro constant,
NA, which has a value of }}.
Rationale
Why use amount of substance instead of
mass or
volume to tell how much of a substance there is? This is because in
chemical reactions, the reagents react
molecule-to-molecule, ion-to-ion, etc. Since different atoms and therefore molecules have different masses, 100 grams of some substance isn't same amount of some other substance. For example, 100 grams of
carbon has more molecules than 100 grams of
oxygen.
See:
Stoichiometry
Terminology
When quoting an amount of substance, it's necessary to specify the entity involved (unless there's no risk of ambiguity). One mole of
chlorine could refer either to chlorine atoms (as in 58.44 g of
sodium chloride) or to chlorine molecules (as in of chlorine gas at
STP). The simplest way to avoid ambiguity is to replace the term "substance" by the name of the entity and/or to quote the
empirical formula. For example:
» amount of
chloroform, CHCl
3
amount of
sodium, Na
» amount of
hydrogen (atoms), H
n(
C2H4)
This can be considered to be a technical definition of the word "amount", a usage which is also found in the names of certain derived quantities (see below).
Derived quantities
When amount of substance enters into a
derived quantity, it's usually as the denominator: such quantities are known as "
molar quantities". For example, the quantity which describes the volume occupied by a given amount of substance is called the
molar volume, while the quantity which describes the mass of a given amount of substance is the
molar mass. Molar quantities are sometimes denoted by a subscript latin "m" in the symbol, except in
clinical chemistry where "substance concentration" is the preferred term (to avoid any possible ambiguity with
mass concentration). The name "molar concentration" is incorrect, if commonly used.
Further Information
Get more info on 'Amount Of Substance'.
|
External Link Exchanges
Do you know how hard it is to get a link from a large encyclopaedia? Well we're different and will prove it. To get a link from us just add the following HTML to your site on a relevant page:
<a href="http://amount_of_substance.totallyexplained.com">Amount of substance Totally Explained</a>
Then simply click through this link from your web page. Our crawlers will verify your link, extract the title of your web page and instantly add a link back to it. If you like you can remove the words Totally Explained and embed the link in article text.
As long as your link remains in place, we'll keep our link to you right here. Please play fair - our crawlers are watching. Your site must be closely related to this one's topic. Any kind of spamming, dubious practises or removing the link will result in your link from us being dropped and, potentially, your whole site being banned. |
