who spent his entire academic career
at Yale University. During the 1870s
he developed the theory of chemical
thermodynamics, devising functions
such as Gibbs *free energy; he also
derived the *phase rule. In mathematics he introduced vector notation.
Gibbs–Duhem equation An equation describing the relation between
the chemical potentials of species in
a mixture. If n i is the amount of
species i and µ i is the chemical potential of species i, the Gibbs–Duhem
equation states that
∑
i
n i dµ i = 0
This equation implies that the chemical potentials for the species in a
mixture do not change independently. Thus, in the case of a binary
mixture, if the chemical potential of
one species increases, the chemical
potential of the other species must
decrease. The equation was derived
independently by J. W. *Gibbs and
the French physicist P. Duhem
(1861–1916).
Gibbs free energy (Gibbs function)
See free energy.
Gibbs–Helmholtz equation An
equation used in thermodynamics to
show the temperature dependence of
the *Gibbs free energy. It has the
form:
(∂G/∂T) p = (G – H)/T,
where G is the Gibbs free energy, H is
the enthalpy, T is the thermodynamic temperature, and p is the pressure (which is held constant). The
Gibbs–Helmholtz equation can be derived from (∂G/∂T) p = – S and S = (H –
G)T using the rules of differentiation.
The equation was derived by J. W.
*Gibbs and H. L. F. von *Helmholtz.
gibbsite A mineral form of hydrated *aluminium hydroxide
(Al(OH) 3 ). It is named after the US
mineralogist George Gibbs (d. 1833).
giga- Symbol G. A preÜx used in the
metric system to denote one thousand million times. For example, 10
9
joules = 1 gigajoule (GJ).
gilbert Symbol Gb. The c.g.s. unit
of magnetomotive force equal to
10/4π (= 0.795 77) ampere-turn. It is
named after the English physician
and physicist William Gilbert
(1544–1603), who studied magnetism.
glacial ethanoic acid See
ethanoic acid.
glass Any noncrystalline solid; i.e. a
solid in which the atoms are random
and have no long-range ordered pattern. Glasses are often regarded as supercooled liquids. Characteristically
they have no deÜnite melting point,
but soften over a range of temperatures.
The common glass used in windows, bottles, etc., is soda glass,
which is made by heating a mixture
of lime (calcium oxide), soda (sodium
carbonate), and sand (silicon(IV)
oxide). It is a form of calcium silicate.
Borosilicate glasses (e.g. Pyrex) are
made by incorporating some boron
oxide, so that silicon atoms are replaced by boron atoms. They are
tougher than soda glass and more resistant to temperature changes,
hence their use in cooking utensils
and laboratory apparatus. Glasses for
special purposes (e.g. optical glass)
have other elements added (e.g. barium, lead). See also spin glass.
glass electrode A type of *half
cell having a glass bulb containing an
acidic solution of Üxed pH, into
which dips a platinum wire. The
glass bulb is thin enough for hydrogen ions to diffuse through. If the
bulb is placed in a solution containing hydrogen ions, the electrode potential depends on the hydrogen-ion
Gibbs–Duhem equation
246
g
www.AzShimi.ir www.AzShimi.com
at Yale University. During the 1870s
he developed the theory of chemical
thermodynamics, devising functions
such as Gibbs *free energy; he also
derived the *phase rule. In mathematics he introduced vector notation.
Gibbs–Duhem equation An equation describing the relation between
the chemical potentials of species in
a mixture. If n i is the amount of
species i and µ i is the chemical potential of species i, the Gibbs–Duhem
equation states that
∑
i
n i dµ i = 0
This equation implies that the chemical potentials for the species in a
mixture do not change independently. Thus, in the case of a binary
mixture, if the chemical potential of
one species increases, the chemical
potential of the other species must
decrease. The equation was derived
independently by J. W. *Gibbs and
the French physicist P. Duhem
(1861–1916).
Gibbs free energy (Gibbs function)
See free energy.
Gibbs–Helmholtz equation An
equation used in thermodynamics to
show the temperature dependence of
the *Gibbs free energy. It has the
form:
(∂G/∂T) p = (G – H)/T,
where G is the Gibbs free energy, H is
the enthalpy, T is the thermodynamic temperature, and p is the pressure (which is held constant). The
Gibbs–Helmholtz equation can be derived from (∂G/∂T) p = – S and S = (H –
G)T using the rules of differentiation.
The equation was derived by J. W.
*Gibbs and H. L. F. von *Helmholtz.
gibbsite A mineral form of hydrated *aluminium hydroxide
(Al(OH) 3 ). It is named after the US
mineralogist George Gibbs (d. 1833).
giga- Symbol G. A preÜx used in the
metric system to denote one thousand million times. For example, 10
9
joules = 1 gigajoule (GJ).
gilbert Symbol Gb. The c.g.s. unit
of magnetomotive force equal to
10/4π (= 0.795 77) ampere-turn. It is
named after the English physician
and physicist William Gilbert
(1544–1603), who studied magnetism.
glacial ethanoic acid See
ethanoic acid.
glass Any noncrystalline solid; i.e. a
solid in which the atoms are random
and have no long-range ordered pattern. Glasses are often regarded as supercooled liquids. Characteristically
they have no deÜnite melting point,
but soften over a range of temperatures.
The common glass used in windows, bottles, etc., is soda glass,
which is made by heating a mixture
of lime (calcium oxide), soda (sodium
carbonate), and sand (silicon(IV)
oxide). It is a form of calcium silicate.
Borosilicate glasses (e.g. Pyrex) are
made by incorporating some boron
oxide, so that silicon atoms are replaced by boron atoms. They are
tougher than soda glass and more resistant to temperature changes,
hence their use in cooking utensils
and laboratory apparatus. Glasses for
special purposes (e.g. optical glass)
have other elements added (e.g. barium, lead). See also spin glass.
glass electrode A type of *half
cell having a glass bulb containing an
acidic solution of Üxed pH, into
which dips a platinum wire. The
glass bulb is thin enough for hydrogen ions to diffuse through. If the
bulb is placed in a solution containing hydrogen ions, the electrode potential depends on the hydrogen-ion
Gibbs–Duhem equation
246
g
www.AzShimi.ir www.AzShimi.com