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Chemical Reactions Essay, Research Paper

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:

nH2OC(C6H4)CO2H + nHOCH2CH2OH -* [...OC(C6H4)CO2CH2CH2O...]n

+ 2nH2O

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:

H2 + 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

triflouride:

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 + H2 -* 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

chloride:

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:

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