Encyclopedia of Chemistry

available for transcription, while heterochromatin is
denser and usually is not transcribed.

eudismic ratio The POTENCYof the EUTOMERrela-
tive to that of the DISTOMER.

eukaryote Organism whose cells have their GENETIC
material packed in a membrane-surrounded, struc-
turally discrete nucleus, and that have well-developed
cell organelles.

eutomer The ENANTIOMERof a CHIRALcompound
that is the more potent for a particular action.
See alsoDISTOMER.

eutrophication The accelerated loading or dumping
of nutrients in a lake by natural or human-induced
causes. Natural eutrophication will change the charac-
ter of a lake very gradually, sometimes taking centuries,
but human-induced or cultural eutrophication speeds
up the aging of a lake, changing its qualities quickly,
often in a matter of years.

eutrophic lake Any lake that has an excessive supply
of nutrients, usually nitrates and phosphates. Eutrophic
lakes are usually not deep, contain abundant algae or
rooted plants, and contain limited oxygen in the bot-
tom layer of water.

evaporation When surface molecules of liquids
break loose of the intermolecular forces that hold them
in the liquid and enter the vapor phase.

evaporative cooling Temperature reduction that
occurs when water absorbs latent heat from the sur-
rounding air as it evaporates; cooling of the skin from
the evaporation of sweat is evaporative cooling and is a
process for the body to lose excess heat.

evapotranspiration The sum of evaporation and
plant transpiration. Potential evapotranspiration is the

amount of water that could be evaporated or tran-

spired at a given temperature and humidity when there

is plenty of water available. Actual evapotranspiration

cannot be any greater than precipitation, and will usu-

ally be less because some water will run off in rivers

and flow to the oceans. If potential evapotranspiration

is greater than actual precipitation, then soils are

extremely dry during at least a major part of the year.

Ewens-Bassett number SeeOXIDATION NUMBER.

EXAFS See EXTENDED X-RAY ABSORPTION FINE

STRUCTURE.

excess acidity See BUNNETT-OLSEN EQUATIONS;

COX-YATES EQUATION.

excimer An excited dimer, “nonbonding” in the

GROUND STATE. For example, a complex formed by the

interaction of an excited MOLECULAR ENTITYwith a

ground-state counterpart of this entity.

See alsoEXCIPLEX.

exciplex An electronically excited complex of defi-

nite stoichiometry, “nonbonding” in the GROUND

STATE. For example, a complex formed by the interac-

tion of an excited MOLECULAR ENTITYwith a ground-

state counterpart of a different structure.

See alsoEXCIMER.

exciplex 101

Evaporation. When surface molecules of liquids break loose of

the intermolecular forces that hold them in the liquid and enter

the vapor phase