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: 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

and heat.

Endoergic, or endothermic, reactions absorb energy during

the reaction. The melting of an ice cube is an example of an

endothermic reaction.

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

reaction.

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 + 6H2O

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

the reaction.

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

chemistry.