EDTA Ethylenediaminetetraacetic
acid,
(HOOCCH 2 ) 2 N(CH 2 ) 2 N(CH 2 COOH) 2 ,a compound that acts as a chelating
agent, reversibly binding with iron,
magnesium, and other metal ions. It
is used in certain culture media
bound with iron, which it slowly re-
leases into the medium, and also in
some forms of quantitative analysis.
EELS(electron energy loss spec-
troscopy) A technique for studying
adsorbates and their dissociation. A
beam of electrons is reÛected from a
surface and the energy loss they suf-
fer upon reÛection is measured. This
loss can be used to interpret the vi-
brational spectrum of the adsorbate.
Very small amounts of adsorbate can
be detected using EELS (as few as 50
atoms in a sample); this is particu-
larly useful for light elements that
are not readily detected using other
techniques.
effervescence The formation of
gas bubbles in a liquid by chemical
reaction.
efÜciencyA measure of the perfor-
mance of a machine, engine, etc.,
being the ratio of the energy or
power it delivers to the energy or
power fed to it. In general, the efÜ-
ciency of a machine varies with the
conditions under which it operates
and there is usually a load at which it
operates with the highest efÜciency.
The thermal efÜciencyof a heat en-
gine is the ratio of the work done by
the engine to the heat supplied by
the fuel. For a reversible heat engine
this efÜciency equals (T 1 – T 2 )/T 1 ,
where T 1 is the thermodynamic tem-
perature at which all the heat is
taken up and T 2 is the thermody-
namic temperature at which it is
given out (see carnot cycle). For real
engines it is always less than this.
efÛorescence The process in
which a crystalline hydrate loses
water, forming a powdery deposit on
the crystals.effusion TheÛow of a gas through
a small aperture. The relative rates at
which gases effuse, under the same
conditions, is approximately in-
versely proportional to the square
roots of their densities.Ehrenfest classiÜcationA
classiÜcation of phase transitions in
terms of their thermodynamic prop-
erties put forward by the Dutch
physicist Paul Ehrenfest (1880–1933).
A Ürst-order phase transition is a
phase transition in which theÜrst de-
rivative of the chemical potential is
discontinuous. In aÜrst-order phase
transition there is a nonzero change
in the value of the enthalpy, entropy,
and volume at the transition temper-
ature. Melting and boiling are exam-
ples ofÜrst-order phase transitions.
In a second-order phase transition,
theÜrst derivative of the chemical
potential is continuous but its second
derivative is not continuous. In a sec-
ond-order phase transition there is
no jump in the value of the enthalpy,
entropy, and volume at the transition
temperature. Examples of second-
order phase transitions include the
transition to ferromagnetism and
order–disorder transitions in alloys.Ehrlich’s reagent See p-dimethyl-
aminobenzadehyde.
eigenfunctionIn general, a solu-
tion of an *eigenvalue equation. In
*quantum mechanics eigenfunctions
occur as the allowed wave functions
of a system and so satisfy the
*Schrödinger equation.
eigenvaluesThe allowed set of val-
ues of the constants in an eigenvalue
equation. In an eigenvalue equation
the left-hand side consists of an oper-
ator and an *eigenfunction, upon
which the operator operates; the191 eigenvalues
e