Physical constant: Electric charge of one mole of electrons
Not to be confused with
farad
.
Faraday constant
|
---|
![](//upload.wikimedia.org/wikipedia/commons/thumb/d/da/Michael_Faraday_%281791-1867%29.jpg/220px-Michael_Faraday_%281791-1867%29.jpg) |
Common symbols
| F
|
---|
SI unit
| coulomb per mole (C/mol)
|
---|
In
SI base units
| s?A?mol
?1
|
---|
Derivations from
other quantities
| F
=
eN
A
|
---|
Value
| 9.648
533
212
331
001
84
×
10
4
C⋅mol
?1
|
---|
In
physical chemistry
, the
Faraday constant
(symbol
F
, sometimes stylized as ?) is a
physical constant
defined as the quotient of the total
electric charge
(
q
) by the
amount
(
n
) of
elementary charge carriers
in any given sample of matter:
F
=
q
/
n
;
it is expressed in
units
of
coulombs
per
mole
(C/mol).
As such, it represents the "
molar
elementary charge
",
[1]
that is, the electric charge of one mole of elementary carriers (e.g., protons). It is named after the English
scientist
Michael Faraday
. Since the
2019 redefinition of SI base units
,
[1]
the Faraday constant has an exactly-defined value, the product of the elementary charge (
e
, in coulombs) and the
Avogadro constant
(
N
A
, in reciprocal moles):
- F
=
e
×
N
A
- =
1.602
176
634
×
10
?19
C
×
6.022
140
76
×
10
23
mol
?1
- =
9.648
533
212
331
001
84
×
10
4
C⋅mol
?1
.
Derivation
[
edit
]
The Faraday constant can be thought of as the conversion factor between the mole (used in chemistry) and the
coulomb
(used in physics and in practical electrical measurements), and is therefore of particular use in
electrochemistry
. Because there are exactly
N
A
=
6.022
140
76
×
10
23
entities per mole,
[1]
and there are exactly
1
/
e
=
10
19
/
1.602
176
634
elementary charges per coulomb,
[1]
the Faraday constant is given by the quotient of these two quantities:
- F
=
N
A
/
1/
e
=
9.648
533
212
331
001
84
×
10
4
C⋅mol
?1
.
One common use of the Faraday constant is in
electrolysis
calculations. One can divide the amount of charge (the current integrated over time) by the Faraday constant in order to find the
chemical amount
of a substance (in moles) that has been electrolyzed.
The value of
F
was first determined in the 1800s by weighing the amount of
silver
deposited in an electrochemical reaction, in which a measured
current
was passed for a measured time, and using
Faraday's law of electrolysis
.
[2]
Until about 1970, the most reliable value of the Faraday constant was determined by a related method of electro-dissolving silver metal in
perchloric acid
.
[3]
Other common units
[
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]
- 96.485 kJ per volt?gram-equivalent
- 23.061 kcal per volt?gram-equivalent
- 26.801 A·h/mol
Faraday ? a unit of charge
[
edit
]
Related to the Faraday constant is the "faraday", a unit of
electrical charge
. Its use is much less common than of the
coulomb
, but is sometimes used in electrochemistry.
[4]
One faraday of charge is the charge of one mole of
elementary charges
(or of negative one mole of electrons), that is,
- 1 faraday =
F
× 1 mol =
9.648
533
212
331
001
84
×
10
4
C
Conversely, the Faraday constant
F
equals 1 faraday per mole.
The faraday is not to be confused with the
farad
, an unrelated unit of
capacitance
(
1 farad = 1 coulomb / 1 volt
).
Popular media
[
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]
The Simpsons
episode "
Dark Knight Court
" has
Mr. Burns
asking
Comic Book Guy
how much he wants for his entire
comic book
inventory. He says "the
speed of light
expressed as
dollars
" and Mr. Burns tells Smithers to "just give him Faraday's Constant". The check is written for $96,485.34.
See also
[
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]
References
[
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]