atomite)A softÜne-grained deposit
consisting of the siliceous skeletal re-
mains of diatoms, formed in lakes
and ponds. Kieselguhr is used as an
absorbent,Ültering material,Üller,
and insulator.
kieserite A mineral form of *mag-
nesium sulphate monohydrate,
MgSO 4 .H 2 O.
kilo- Symbol k. A preÜx used in the
metric system to denote 1000 times.
For example, 1000 volts = 1 kilovolt
(kV).
kilogramSymbol kg. The *SI unit
of mass deÜned as a mass equal to
that of the international platinum–
iridium prototype kept by the Inter-
national Bureau of Weights and
Measures at Sèvres, near Paris.
kimberliteA rare igneous rock
that often contains diamonds. It oc-
curs as narrow pipe intrusions but is
often altered and fragmented. It con-
sists of olivine and phlogopite mica,
usually with calcite, serpentine, and
other minerals. The chief occur-
rences of kimberlite are in South
Africa, especially at Kimberley (after
which the rock is named), and in the
Yakutia area of Siberia.
kinematic viscosity Symbol ν.
The ratio of the *viscosity of a liquid
to its density. The SI unit is m^2 s–1.
kinetic effect A chemical effect
that depends on reaction rate rather
than on thermodynamics. For exam-
ple, diamond is thermodynamically
less stable than graphite; its apparent
stability depends on the vanishingly
slow rate at which it is converted.
*Overpotential in electrolytic cells is
another example of a kinetic effect.
Kinetic isotope effects are changes in
reaction rates produced by isotope
substitution. For example, if the slow
step in a chemical reaction is the
breaking of a C–H bond, the rate for
the deuterated compound would be
slightly lower because of the lower
vibrational frequency of the C–D
bond. Such effects are used in investi-
gating the mechanisms of chemical
reactions.kinetic energySee energy.kinetic isotope effect See kinetic
effect.kineticsThe branch of physical
chemistry concerned with measuring
and studying the rates of chemical
reactions. The main aim of chemical
kinetics is to determine the mecha-
nism of reactions by studying the
rate under different conditions (tem-
perature, pressure, etc.). See also acti-
vated-complex theory; arrhenius
equation.kinetic theoryA theory, largely
the work of Count *Rumford, James
Prescott *Joule, and James Clerk
*Maxwell, that explains the physical
properties of matter in terms of the
motions of its constituent particles.
In a gas, for example, the pressure is
due to the incessant impacts of the
gas molecules on the walls of the
container. If it is assumed that the
molecules occupy negligible space,
exert negligible forces on each other
except during collisions, are perfectly
elastic, and make only brief collisions
with each other, it can be shown that
the pressure p exerted by one mole
of gas containing n molecules each of
mass m in a container of volume V,
will be given by:
p = nmc_ 2
/3V,
where c_
c^2 is the mean square speed
of the molecules. As according to the
*gas laws for one mole of gas: pV =
RT, where T is the thermodynamic
temperature, and R is the molar *gas
constant, it follows that:
RT = nmc_ 2
/3
Thus, the thermodynamic tempera-305 kinetic theory
k