Chemical Reaction & Information
Description of Chemical Reactions;
||Reactions are the verbs of chemistry. The activity that chemists
study. Many reactions move to their conclusion and then stop,
meaning that the reactants have been completely transformed into products, with
no means of returning to their original state. In some cases, the reaction
truly is irreversible, as for instance when combustion changes both the
physical and chemical properties of a substance. There are plenty of other
circumstances, however, in which a reverse reaction is not only possible but an
ongoing process, as the products of the first reaction become the reactants in
a second one. This dynamic state, in which the concentration of reactants and
products remains constant, is referred to as equilibrium. It is possible to
predict the behavior of substances in equilibrium through the use of certain
laws, which are applied in industries seeking to lower the costs of producing
specific chemicals. Equilibrium is also useful in understanding processes that
preserve or potentially threaten human health.
A chemical reaction is a process whereby the chemical
properties of a substance are altered by a rearrangement of the atoms in the
substance. The changes produced by a chemical reaction are fundamentally
different from physical changes, such as boiling or melting liquid water,
changes that alter the physical properties of water without affecting its
molecular structure.
Though chemical reactions are most effectively analyzed in
terms of molecular properties and behaviors, there are numerous indicators that
suggest to us when a chemical reaction has occurred. It is unlikely that all of
these will result from any one reaction, and in fact chances are that a
particular reaction will manifest only one or two of these effects.
Nonetheless, these offer us hints that a reaction has taken place.
Signs that a substance has undergone a chemical reaction:
Water is produced, A solid forms, Gases are produced,
Bubbles are formed, There is a change in color, The temperature changes, the
taste of a consumable substance changes, The smell changes.
Many of these effects can be produced simply by changing the
temperature of a substance, but again, the mere act of applying heat from
outside (or removing heat from the substance itself) does not constitute a
chemical change. Water can be produced by melting ice, but the water was
already there it only changed form. By contrast, when an acid and a base react
to form water and a salt, that is a true chemical reaction.
Similarly, the freezing of water forms a solid, but no new
chemical substance has been formed. In a chemical reaction by contrast, two liquids
can react to form a solid. When water boils through the application of heat,
bubbles form, and a gas or vapor is produced; yet in chemical changes, these
effects are not the direct result of applying heat.
In this context, a change in temperature, noted as another
sign that a reaction has taken place, is a change of temperature from within
the substance itself. Chemical reactions can be classified as heat producing
(exothermic) or heat absorbing (endothermic). In either case, the transfer of
heat is not accomplished simply by creating a temperature differential, as
would occur if heat were transferred merely through physical means.
At one time, chemists could only study reactions from the
outside, as it were, purely in terms of effects noticeable through the senses.
Between the early nineteenth and the early twentieth century, however, the
entire character of chemistry changed, as did the terms in which chemists
discussed reactions. Today, those reactions are analyzed primarily in terms of
subatomic, atomic, and molecular properties and activities.
Despite all this progress, however, chemists still do not
know exactly what happens in a chemical reaction but they do have a good
approximation. This is the collision model, which explains chemical reactions in
terms of collisions between molecules. If the collision is strong enough, it
can break the chemical bonds in the reactants, resulting in a re formation of
atoms within different molecules. The more the molecules collide, the more
bonds are being broken, and the faster the reaction.
Considering all other kinetic parameters constant, an
increase in the numbers of collisions can be produced in two ways: either the
concentrations of the reactants are increased, or the temperature is increased.
By raising the temperature, the speeds of the molecules themselves increase,
and the collisions possess more energy. A certain energy threshold, the
activation energy must be crossed in order for a reaction to occur. A
temperature increase raises the likelihood that a given collision will cross
the activation energy threshold, producing the energy to break the molecular
bonds and promote the chemical reaction.
Raising the temperature and the concentrations of reactants
can increase the energy and hasten the reactions, but in some cases it is not
possible to do either. Fortunately, the rate of reaction can be increased in a
third way, through the introduction of a catalyst, a substance that speeds up
the reaction without participating in it either as a reactant or product.
A chemical equation, like a mathematical equation,
symbolizes an interaction between entities that produces a particular result.
In the case of a chemical equation, the entities are not numbers but reactants,
and they interact with each other not through addition or multiplication, but
by chemical reaction. Yet just as a product is the result of multiplication in
mathematics, a product in a chemical equation is the substance or substances
that result from the reaction.
Instead of an equals sign, between the reactants and the
product, arrows are used. When the arrow points to the right, this indicates a
forward reaction; conversely, an arrow pointing to the left symbolizes a
reverse reaction. In a reverse reaction, the products of a forward reaction
have become the reactants, and the reactants of the forward reaction are now
the products.
Chemical equilibrium, which occurs when the ratio between
the reactants and products is constant and in which the forward and reverse
reactions take place at the same rate.
Chemical equations usually include notation indicating the
state or phase of matter for the reactants and products: (s) for a solid; (l)
for a liquid; (g) for a gas. A fourth symbol, (aq), indicates a substance
dissolved in water that is, an aqueous solution.
Not all situations of equilibrium are alike: depending on
certain factors, the position of equilibrium may favor one side of the equation
or the other. If a company is producing chemicals for sale, for example, its
production managers will attempt to influence reactions in such a way as to
favor the forward reaction. In such a situation, it is said that the
equilibrium position has been shifted to the right. In terms of physical
equilibrium, mentioned above, this would be analogous to what would happen if
you were holding your arms out on either side of your body, with a heavy lead
weight in your left hand and a much smaller weight in the right hand.
Your center of gravity, or equilibrium position, would shift
to the left to account for the greater force exerted by the heavier weight.
Suppose we add more of a particular substance to increase
the rate of the forward reaction. In an equation for this reaction, the
equilibrium symbol is altered, with a longer arrow pointing to the right to
indicate that the forward reaction is favored. Again, the equilibrium position
has shifted to the right just as one makes physical adjustments to account for
an imbalanced weight. The system responds by working to consume more of the
reactant, thus adjusting to the stress that was placed on it by the addition of
more of that substance. By the same token, if we were to remove a particular
reactant or product, the system would shift in the direction of the detached
component.
If the volume of gases in a closed container is decreased,
the pressure increases. An equilibrium system will therefore shift in the
direction that reduces the pressure; but if the volume is increased, thus
reducing the pressure, the system will respond by shifting to increase
pressure.
However, that not all increases in pressure lead to a shift
in the equilibrium. If the pressure were increased by the addition of a noble
gas, the gas itself since these elements are noted for their lack of reactivity
would not be part of the reaction. Thus the species added would not be part of
the equilibrium constant expression, and there would be no change in the
equilibrium.
In an exothermic, or
heat-producing reaction, the heat is treated as a product. Thus, when nitrogen
and hydrogen react, they produce not only ammonia, but a certain quantity of
heat. If this system is at equilibrium, Le Chatelier's principle shows that the
addition of heat will induce a shift in equilibrium to the left in the
direction that consumes heat or energy.
The reverse is true in an endothermic, or heat-absorbing
reaction. Chemical reactions involve the making and breaking of bonds. It is
essential that we know what bonds are before we can understand any chemical
reaction. To understand bonds, we will first describe several of their
properties. The bond strength tells us how hard it is to break a bond. Bond
lengths give us valuable structural information about the positions of the
atomic nuclei. Bond dipoles inform us about the electron distribution around
the two bonded atoms. From bond dipoles we may derive electronegativity data
useful for predicting the bond dipoles of bonds that may have never been made
before.
From these properties of bonds we will see that there are
two fundamental types of bonds covalent and ionic. Covalent bonding represents
a situation of about equal sharing of the electrons between nuclei in the bond.
Covalent bonds are formed between atoms of approximately equal
electronegativity. Because each atom has near equal pull for the electrons in
the bond, the electrons are not completely transferred from one atom to
another. When the difference in electronegativity between the two atoms in a
bond is large, the more electronegative atoms that can strip an electron off,
of the less electronegative one, to form a negatively charged anion and a
positively charged cation. The two ions are held together in an ionic bond
because the oppositely charged ions attract each other, when in the solid
state, can be described as ionic lattices whose shapes are dictated by the need
to place oppositely charged ions close to each other and similarly charged ions
as far apart as possible. Though there is some structural diversity in ionic
compounds, covalent compounds present us with a world of structural
possibilities.
Conclusively, the number of possibilities of new chemical
reactions for the industry is greatly enhanced by the capacity of modern
computers.
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How little change in small scale makes big different in
large scale?!
It is Dynamic System. The system that always its elements
are moving and there is no rule & role how to move!
It is always Chaotic.
Because of this we get, How DNA strings shape live organs
and How simple bits of information generate complex system.
But we can predict what happen in the end of chemical
reactions. For example if we mix A and B we can predict to have AB. However we
can guess correctly results of reactions But we cannot mark each element. We
can guess about congeries of materials. Even if we suppose that can mark some
molecules we cannot mark electrons and of course we cannot predict about spins
of electrons.
Chemical Reactions are depend on electrons when you observe
them in small scale (on classical physics).
String of Information becomes observable at first step of
classical viewpoint on spin & wave.
At second step its spinal state that shapes our universe;
life & another structures.
But at the first step it is information, that can be stored
on spinal state, atoms, molecules, wave state, quarks, sea, mountain, cells,
trees, … & nothing!
When you chemically mix A & B it changes their
structures so their information generate new structure with new properties and
features it is How DNA can build completely new structure: with new internal
& external features.
To be continue…
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