H 2 O(g) + C(s) →CO(g) + H 2 (g)
The reaction is strongly endothermic
but the reaction can be used in con-
junction with that for *producer gas
for making fuel gas. The main use of
water gas before World War II was in
producing hydrogen for the *Haber
process. Here the above reaction was
combined with the water-gas shift
reaction to increase the amount of
hydrogen:
CO + H 2 O ˆCO 2 + H 2
Most hydrogen for the Haber process
is now made from natural gas by
steam *reforming.
water glassA viscous colloidal so-
lution of sodium silicates in water,
used to make silica gel and as a size
and preservative.water of crystallizationWater
present in crystalline compounds in
deÜnite proportions. Many crystalline
salts form hydrates containing 1, 2,
3, or more moles of water per mole
of compound, and the water may be
held in the crystal in various ways.
Thus, the water molecules may sim-
ply occupy lattice positions in the
crystal, or they may form bonds with
the anions or the cations present. In
the pentahydrate of copper sulphate
(CuSO 4 .5H 2 O), for instance, each cop-
per ion is coordinated to four water
molecules through the lone pairs on
the oxygen to form the *complex
[Cu(H 2 O) 4 ]2+. Each sulphate ion has
one water molecule held by hydro-
gen bonding. The difference between
the two types of bonding is demon-
strated by the fact that the pentahy-
drate converts to the monohydrate at
100 °C and only becomes anhydrous
above 250°C. Water of constitution is
an obsolete term for water combined
in a compound (as in a metal hydrox-
ide M(OH) 2 regarded as a hydrated
oxide MO.H 2 O).water softeningSee hardness of
water.wattSymbol W. The SI unit of
power, deÜned as a power of one
joule per second. In electrical con-
texts it is equal to the rate of energy
transformation by an electric current
of one ampereÛowing through a
conductor the ends of which are
maintained at a potential difference
of one volt. The unit is named after
James Watt (1736–1819).wave equationA partial differen-
tial equation of the form:
∇^2 u = (1/c^2 )∂^2 u/∂t^2 ,
where
∇^2 = ∂^2 /∂x^2 + ∂^2 /∂y^2 + ∂^2 /∂z^2
is the Laplace operator. It represents
the propagation of a wave, where u is
the displacement and c the speed of
propagation. See also schrödinger
equation.wave functionA function ψ(x,y,z)
appearing in *Schrödinger’s equation
in wave mechanics. The wave func-
tion is a mathematical expression in-
volving the coordinates of a particle
in space. If the Schrödinger equation
can be solved for a particle in a given
system (e.g. an electron in an atom)
then, depending on the boundary
conditions, the solution is a set of
allowed wave functions (eigen-
functions) of the particle, each cor-
responding to an allowed energy
level (eigenvalue). The physical
signiÜcance of the wave function is
that the square of its absolute value,
|ψ|^2 , at a point is proportional to the
probability ofÜnding the particle in a
small element of volume, dxdydz, at
that point. For an electron in an
atom, this gives rise to the idea of
atomic and molecular *orbitals.wave mechanicsA formulation of
*quantum mechanics in which the
dual wave–particle nature of such en-water glass 554w