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Chemical reactions are the heart of chemistry. People have
always known that they exist. The Ancient Greeks were the firsts
to speculate on the composition of matter. They thought that it
was possible that individual particles made up matter.
Later, in the Seventeenth Century, a German chemist named
Georg Ernst Stahl was the first to postulate on chemical
reaction, specifically, combustion. He said that a substance
called phlogiston escaped into the air from all substances during
combustion. He explained that a burning candle would go out if a
candle snuffer was put over it because the air inside the snuffer
became saturated with phlogiston. According to his ideas, wood
is made up of phlogiston and ash, because only ash is left after
combustion. His ideas soon came upon some contradiction. When
metal is burned, its ash has a greater mass than the original
substance. Stahl tried to cover himself by saying that
phlogiston will take away from a substance’s mass or that it had
a negative mass, which contradicted his original theories.
In the Eighteenth Century Antoine-Laurent Lavoisier, in
France, discovered an important detail in the understanding of
the chemical reaction combustion, oxigine (oxygen). He said that
combustion was a chemical reaction involving oxygen and another
combustible substance, such as wood.
John Dalton, in the early Nineteenth Century, discovered the
atom. It gave way to the idea that a chemical reaction was
actually the rearrangement of groups of atoms called molecules.
Dalton also said that the appearance and disappearance of
properties meant that the atomic composition dictated the
appearance of different properties. He also came up with idea
that a molecule of one substance is exactly the same as any other
molecule of the same substance.
People like Joseph-Lois Gay-Lussac added to Dalton’s
concepts with the postulate that the volumes of gasses that react
with each other are related (14 grams of nitrogen reacted with
exactly three grams of hydrogen, eight grams of oxygen reacted to
exactly one gram of hydrogen, etc.)
Amedeo Avogadro also added to the understanding of chemical
reactions. He said that all gasses at the same pressure, volume
and temperature contain the same number of particles. This idea
took a long time to be accepted. His ideas lead to the
subscripts used in the formulas for gasses.
From the work of these and many other chemists, we now have
a mostly complete knowledge of chemical reactions. There are now
many classification systems to classify the different types of
reactions. These include decomposition, polymerization, chain
reactions, substitute reactions, elimination reactions, addition
reactions, ionic reactions, and oxidation-reduction reactions.
Decomposition reactions are reactions in which a substance
breaks into smaller parts. As an example, ammonium carbonate
will decompose into ammonia, carbon dioxide, and water.
Polymerization reactions are reactions in which simpler
substances combine to form a complex substance. The thing that
makes this reaction unusual is that the final product is composed
of hundreds of the simpler reagent (a substance that contributes
to a chemical reaction) species. One example is the
polymerization of terephthalic acid with ethylene glycol to form
the polymer called Dacron, a fibre, or Mylar, in sheet form:
nH3OC(C6H4)CO2H + nHOCH3CH3OH -* [...OC(C6H4)CO2CH3CH3O...]n
in which n is a large number of moles. A chain reaction is a
series of smaller reactions in which the previous reaction forms
a reagent for the next reaction. The synthesis of hydrogen
bromide is a good example:
H3 + Br2 -* 2HBr
This is a simple equation that doesn’t properly prove the
reaction. It is very complex and starts with this:
Br2 -* 2Br
The next three reactions are related and should be grouped
together. A substation reaction is a reaction in which a
substance loses one or more atoms and replaces them with the same
number of atoms of another element from another substance. Here
is the example of chloroform that reacts with antimony
CHCl3 + SbF3 -* CHClF2
An elimination reaction is a reaction in which a compound is
broken into smaller parts when heated. Here is an example when
the same substance is heated and goes through another reaction:
2CHClF2 -* C2F4 + 2HCl
An addition reaction is a reaction in which atoms are added to a
molecule. If the added atoms are hydrogens, then the reaction is
called a hydrogenization reaction. If Oleic acid is
hydrogenized, this what you get:
C18H34O2 + H3 -* C18H36O2
Another reaction is called an ionic reaction. It occurs
between two ions and can happen very quickly. For example, when
silver nitrate and sodium chloride are mixed you get silver
AgNO3 + NaCl -* AgCl + NaNO3
The last type of reaction is called oxidation-reduction.
These are reactions that involve a change in oxidation number.
It is a reaction if the oxidation number goes up. It is a
reduction reaction if the oxidation number goes down.
It is now known that there are three types of chemical
reactions. They are classified into three types: exoergic
(exothermic), endoergic (endothermic), and aergic (athermic). In
these cases, energy is supplied, but the different types of
reactions initiate the energy differently.
Exoergic, or exothermic, reactions release energy during
the reaction. Combustion is one of the major reactions that do
this. The burning of wood, or any other fuel, gives off heat,
and the burning of glucose in our bodies gives off both energy
Endoergic, or endothermic, reactions absorb energy during
the reaction. The melting of an ice cube is an example of an
Aergic, or athermic, reactions neither give off nor absorb
energy. There are very few cases in which this happens.
There are some things that must be considered in a chemical
reaction. Kinetics is one of these things. Kinetics decides The
speed of the reaction and what is happening on a molecular level.
There are a few things that decide the course and speed of the
The first thing is the reactants. Different reactants react
at different speeds. Even the position of the reactants will
affect the reaction rate.
The next thing is the catalyst that contributes a needed
substance to the reaction. It Is part of the energy
considerations. The catalyst is an outside substance that is
included in the reaction, but is not consumed during the reaction
like the reactants are. They cannot make impossible reactions
occur, they only contribute to the reaction to increase the
reaction rate. There are also such things as negative catalysts,
or inhibitors. Inhibitors retard the reaction rate. This is
also a way to control reactions. A good example in nature of a
catalyst is in a firefly. The reaction that releases the light
is complex. Lucifern, which the firefly makes naturally, is
oxidized in the presence of luciferase, another natural enzyme,
which acts as a catalyst in the reaction. Thus, the reaction
makes an excited form of luciferase, which soon returns to its
original state. Energy as light is released when the lucifrase
returns to its normal state. The insect can easily control this
reaction with an inhibitor it naturally makes.
Another contributor in this consideration is entropy. It is
the measure of energy not available for work in the reaction that
becomes energy moved to disorder. Entropy is simply a
measurement of unusable energy in a closed thermodynamic system.
An acid and base reaction is another thing to consider.
Acids and bases react very readily to each other. When an acid
and a base react, they form water and a salt.
Acids and bases neutralize each other and form a salt as a
byproduct. This reaction reaches what is called equilibria,
(When a substance is completely neutral in charge and acidity).
One example of how acids and bases react is the reaction of
calcium hydroxide and phosphoric acid to produce calcium
phosphate and water:
3Ca(OH)2 + 2H3PO4 -* Ca3(PO4)2 + 6H3O
The last detail is the reaction conditions. The
temperature, humidity, and barometric pressure will affect the
reaction. Even a slight change in any one of these could change
There are many branches of Chemistry that use chemical
reactions, infact, almost all of them. Here are some examples.
Photochemistry is one branch of chemistry that deals with
chemical reactions. It has to do with the radiant energy of all
kinds formed during chemical reactions. Photochemists will
experiment with chemical reactions. They will perform reactions
normally only possible at high temperatures in room temperature
under ultra-violet radiation. The reaction rate can be
controlled for observation by varying the intensity of the
radiation. X-rays and gamma rays are commonly used in these
procedures. The most important photochemical reaction is
photosynthesis. Carbon-dioxide and water combine with chlorophyll
as a catalyst to give off oxygen. Photochemical reactions are
caused by photons that are given off by the light source. The
reactant molecules absorb the photons and get excited. They are
at such an excited state, they can decompose, ionize, cause a
reaction with other molecules, or give off heat.
Another science that uses chemical reactions is
Biochemistry. They use them to produce products that a person
either can’t produce or cannot do as well as they should. The
best example of this the production of insulin. It was first
produced in very tiny beads until someone realized that the body
does in a very similar way. The person was Robert B. Merrifeild.
He was the first to urge scientists to study living systems for
the answers to problems that could be solved with synthesizing
chemical reactions in the body. This was actually the first step
toward the development of bionics.
Scientists today are still toying with chemical reactions.
They are trying to control them with lasers. Scientists are
trying to use lasers to prod a chemical reaction that could go
one way or another, the way they want it to. They want to direct
the molecules in one direction. The control of photons to excite
molecules and cause reactions has been elusive. Recently,
though, chemist Robert J. Gordon at the University of Illinois
achieved “coherent phase control of hydrogen disulfide molecules
by firing ultraviolet lasers of different wavelengths at them.”
Laser chemistry looks promising and is a way that chemistry is
still being expanded. Again, chemical reactions are the main
part of a branch of chemistry.
Here again, scientists are playing with chemical reactions.
In April of 1995, a chemist named Peter Schultz and a physicist
named Paul McEuen of the University of California at Berkly
announced that they could control chemical reactions molecule by
molecule. “The key to the technique is to put a dab of platinum
on the microscopic tip of an atomic force microscope. (The tip
of such a microscope is a tiny cantilever that rides like a
phonograph needle just above the surface of a sample and reacts
to forces exerted by the electrons beneath it.)” The Platinum
acts like a catalyst, stimulating a reaction between two
reactants, just stimulating a reaction one molecule at a time.
The molecules are stimulated in a pattern giving the wanted
results. This discovery opens doors for nanoengineering and
material sciences. It gives a good view of what happens, one
molecule at a time.
Chemical reactions are a large part of chemistry. This
paper is an overveiw of that extensive subject. It gives a good
idea about the history of chemical reactions as well as the
future. Hopefully, there will be no end to the expansion of
chemistry and our knowledge. Since Scientists are still
experimenting, chemical reactions will always be a part of
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