Plasmas
have been described as a fourth state of matter, along with gases,
liquids, and solids at lower temperatures. Electrons and nuclei
from a plasma only combine to form atoms at temperatures below 100,000
degrees. Atoms in turn do not associate into molecules, nor do molecules
condense into liquids and solids, until temperatures fall below
a few thousand degrees. The delicate carbon compounds that we shall
be examining in the following chapters break down a few dozen degrees
above "normal" or room temperature, which can be assumed to be around
300K. In contrast,
most familiar chemical reactions effectively come to a halt 100C
below room temperature.
We saw in Chapter
15 that the rates of chemical reactions depend on energies of
activation. A reaction with a modest activation energy of 11 kcal
mole
proceeds 10,000 times faster at 300
than at 200
, even assuming that it remains a gas-collision process at the lower
temperature. If the reactants and products condense to liquids or
solids, then the process at 200K
is even slower. Just as the familiar physical world is encountered
between 10
cm and 10
cm, so the familiar chemical world occurs primarily between 200K
and 2000K.
Life for some simple bacteria can go on as low as 255K
or as high as 377K,
but for the most advanced organism, man, the chemistry of life breaks
down a short distance to either side of 310K
or 37C. The
more complex the machinery, the more restricted are its operating
conditions.