over porous sintered nickel electrodes. A supply of gaseous hydrogen
is fed to a compartment containing
the porous anode and a supply of
oxygen is fed to a compartment containing the porous cathode; the electrodes are separated by a third
compartment containing a hot alkaline electrolyte, such as potassium
hydroxide. The electrodes are porous
to enable the gases to react with the
electrolyte, with the nickel in the
electrodes acting as a catalyst. At the
anode the hydrogen reacts with the
hydroxide ions in the electrolyte to
form water, with the release of two
electrons per hydrogen molecule:
H 2 + 2OH
–
→ 2H 2 O + 2e
–
At the cathode, the oxygen reacts
with the water, taking up electrons,
to form hydroxide ions:
½O 2 + H 2 O + 2e
–
→ 2OH
–
The electrons Ûow from the anode to
the cathode through an external circuit as an electric current. The device
is a more efÜcient converter of electric energy than a heat engine, but it
is bulky and requires a continuous
supply of gaseous fuels. Their use to
power electric vehicles is being actively explored.
fugacity Symbol f. A thermodynamic function used in place of partial pressure in reactions involving
real gases and mixtures. For a component of a mixture, it is deÜned by dµ
= RTd(lnf), where µ is the chemical
potential. It has the same units as
pressure and the fugacity of a gas is
equal to the pressure if the gas is
ideal. The fugacity of a liquid or solid
is the fugacity of the vapour with
which it is in equilibrium. The ratio
of the fugacity to the fugacity in
some standard state is the *activity.
For a gas, the standard state is chosen to be the state at which the fugacity is 1. The activity then equals
the fugacity.
fullerene See buckminsterfullerene.
fullerite See buckminsterfullerene.
fuller’s earth A naturally occurring clay material (chieÛy montmorillonite) that has the property of
decolorizing oil and grease. In the
past raw wool was cleaned of grease
and whitened by kneading it in
water with fuller’s earth; a process
known as fulling. Fuller’s earth is
now widely used to decolorize fats
and oils and also as an insecticide
carrier and drilling mud. The largest
deposits occur in the USA, UK, and
Japan.
fulminate See cyanic acid.
fulminic acid See cyanic acid.
fumaric acid See butenedioic
acid.
functional group The group of
atoms responsible for the characteristic reactions of a compound. The
functional group is –OH for alcohols,
–CHO for aldehydes, –COOH for carboxylic acids, etc.
fundamental See harmonic.
fundamental constants (universal
constants) Those parameters that do
not change throughout the universe.
The charge on an electron, the speed
of light in free space, the Planck constant, the gravitational constant, the
electric constant, and the magnetic
constant are all thought to be examples.
A
• fundamental physical constants from
NIST
fundamental units A set of independently deÜned *units of measurement that forms the basis of a
fugacity
238
f
www.AzShimi.ir www.AzShimi.com
is fed to a compartment containing
the porous anode and a supply of
oxygen is fed to a compartment containing the porous cathode; the electrodes are separated by a third
compartment containing a hot alkaline electrolyte, such as potassium
hydroxide. The electrodes are porous
to enable the gases to react with the
electrolyte, with the nickel in the
electrodes acting as a catalyst. At the
anode the hydrogen reacts with the
hydroxide ions in the electrolyte to
form water, with the release of two
electrons per hydrogen molecule:
H 2 + 2OH
–
→ 2H 2 O + 2e
–
At the cathode, the oxygen reacts
with the water, taking up electrons,
to form hydroxide ions:
½O 2 + H 2 O + 2e
–
→ 2OH
–
The electrons Ûow from the anode to
the cathode through an external circuit as an electric current. The device
is a more efÜcient converter of electric energy than a heat engine, but it
is bulky and requires a continuous
supply of gaseous fuels. Their use to
power electric vehicles is being actively explored.
fugacity Symbol f. A thermodynamic function used in place of partial pressure in reactions involving
real gases and mixtures. For a component of a mixture, it is deÜned by dµ
= RTd(lnf), where µ is the chemical
potential. It has the same units as
pressure and the fugacity of a gas is
equal to the pressure if the gas is
ideal. The fugacity of a liquid or solid
is the fugacity of the vapour with
which it is in equilibrium. The ratio
of the fugacity to the fugacity in
some standard state is the *activity.
For a gas, the standard state is chosen to be the state at which the fugacity is 1. The activity then equals
the fugacity.
fullerene See buckminsterfullerene.
fullerite See buckminsterfullerene.
fuller’s earth A naturally occurring clay material (chieÛy montmorillonite) that has the property of
decolorizing oil and grease. In the
past raw wool was cleaned of grease
and whitened by kneading it in
water with fuller’s earth; a process
known as fulling. Fuller’s earth is
now widely used to decolorize fats
and oils and also as an insecticide
carrier and drilling mud. The largest
deposits occur in the USA, UK, and
Japan.
fulminate See cyanic acid.
fulminic acid See cyanic acid.
fumaric acid See butenedioic
acid.
functional group The group of
atoms responsible for the characteristic reactions of a compound. The
functional group is –OH for alcohols,
–CHO for aldehydes, –COOH for carboxylic acids, etc.
fundamental See harmonic.
fundamental constants (universal
constants) Those parameters that do
not change throughout the universe.
The charge on an electron, the speed
of light in free space, the Planck constant, the gravitational constant, the
electric constant, and the magnetic
constant are all thought to be examples.
A
• fundamental physical constants from
NIST
fundamental units A set of independently deÜned *units of measurement that forms the basis of a
fugacity
238
f
www.AzShimi.ir www.AzShimi.com