CHEMICAL REACTION

        A chemical reaction is a natural process that always results in inter-change of chemical compounds. Compound or compounds early in the reaction is referred to as the reactants. Chemical reactions are usually characterized by a chemical change, and will produce one or more products that typically have characteristics that are different from the reactants. Classically, chemical reactions involve changes involving the movement of electrons in the forming and breaking of chemical bonds, although the general concept is basically a chemical reaction can also be applied to the transformation of elementary particles such as the nuclear reaction.

Reactions with different chemical used in chemical synthesis to produce the desired compound. In biochemistry, series of chemical reactions catalyzed by enzymes form metabolic pathways, in which the synthesis and decomposition is usually not possible in the cell do.

     Chemical reaction is of a chemical change. In these changes the interaction between chemical compound or chemical element that involves changes in the structure, due to the termination and formation of chemical bonds in the process of energy can be generated and released.

The chemical reaction is written in the form of chemical equations, to more easily remember to note the example of chemical reactions below:

Cu (s) + 2 H2SO4 (aq) → CuSO4 (aq) + 2 H2O (l) + 2 SO2 (g)

From this equation we will get information about substances that react the metals copper and sulfuric acid, producing copper (II) sulfate, water and sulfur dioxide.

This equation also indicates the form of the substance that react, solids with the notation (s), dissolved in water with the notation (aq), (l) liquid and (g) is gas. In addition we also get other information such as mole ratio of the reacting substances and reaction products.



      The reaction of two or more elements together results in the formation of a chemical bond between atoms and the formation of a chemical compound . But why do chemicals react together? The reason has to do with the participating atoms' electron configurations (see our The Periodic Table of Elements module).
In the late 1890s, the Scottish chemist Sir William Ramsay discovered the elements helium, neon, argon, krypton, and xenon. These elements, along with radon, were placed in group VIIIA of the periodic table and nicknamed inert (or noble) gases because of their tendency not to react with other elements (see our Periodic Table page). The tendency of the noble gases to not react with other elements has to do with their electron configurations. All of the noble gases have full valence shells; this configuration is a stable configuration and one that other elements try to achieve by reacting together. In other words, the reason atoms react with each other is to reach a state in which their valence shell is filled.
Let's look at the reaction of sodium with chlorine. In their atomic states, sodium has one valence electron and chlorine has seven.

Sodium Chlorine
Chlorine, with seven valence electrons, needs one additional electron to complete its valence shell with eight electrons. Sodium is a little bit trickier. At first it appears that sodium needs seven additional electrons to complete its valence shell. But this would give sodium a -7 electrical charge and make it highly imbalanced in terms of the number of electrons (negative charges) relative to the number of protons (positive charges). As it turns out, it is much easier for sodium to give up its one valence electron and become a +1 ion. In doing so, the sodium atom empties its third electron shell and now the outermost shell that contains electrons, its second shell, is filled - agreeing with our earlier statement that atoms react because they are trying to fill their valence shell.

Sodium Chloride
     This trait, the tendency to lose electrons when entering into chemical reactions, is common to all metals. The number of electrons metal atoms will lose (and the charge they will take on) is equal to the number of electrons in the atom's valence shell. For all of the elements in group A of the periodic table, the number of valence electrons is equal to the group number (see our Periodic Table page).
Nonmetals, by comparison, tend to gain electrons (or share them) to complete their valence shells. For all of the nonmetals, except hydrogen and helium, their valence shell is complete with eight electrons. Therefore, nonmetals gain electrons corresponding to the formula = 8 - (group #). Chlorine, in group 7, will gain 8 - 7 = 1 electron and form a -1 ion.
Hydrogen and helium only have electrons in their first electron shell.  The capacity of this shell is two.  Thus helium, with two electrons, already has a full valence shell and falls into the group of elements that tend not to react with others, the noble gases.  Hydrogen, with one valence electron, will gain one electron when forming a negative ion.  However, hydrogen and the elements on the periodic table labeled metalloids, can actually form either positive or negative ions corresponding to the number of valence electrons they have.  Thus hydrogen will form a +1 ion when it loses its one electron and a -1 ion when it gains one electron.  

reaction energy

      All chemical reactions are accompanied by a change in energy. Some reactions release energy to their surroundings (usually in the form of heat) and are called exothermic. For example, sodium and chlorine react so violently that flames can be seen as the exothermic reaction gives off heat. On the other hand, some reactions need to absorb heat from their surroundings to proceed. These reactions are called endothermic. A good example of an endothermic reaction is that which takes place inside of an instant '"cold pack." Commercial cold packs usually consist of two compounds - urea and ammonium chloride in separate containers within a plastic bag. When the bag is bent and the inside containers are broken, the two compounds mix together and begin to react. Because the reaction is endothermic, it absorbs heat from the surrounding environment and the bag gets cold.
Reactions that proceed immediately when two substances are mixed together (such as the reaction of sodium with chlorine or urea with ammonium chloride) are called spontaneous reactions. Not all reactions proceed spontaneously. For example, think of a match. When you strike a match you are causing a reaction between the chemicals in the match head and oxygen in the air. The match won't light spontaneously, though. You first need to input energy, which is called the activation energy of the reaction. In the case of the match, you supply activation energy in the form of heat by striking the match on the matchbook; after the activation energy is absorbed and the reaction begins, the reaction continues until you either extinguish the flame or you run out of material to react.

CHARACTERISTICS OF CHEMICAL REACTION
1. Colour Change Happen

In a chemical reaction, reactants are converted into products. Changes may occur due to the termination of the bonds of the reactants and the formation antaratom ties bru that make up the product. Energy required to break the tie. To form a new bond, released some energy. Thus, the chemical reaction energy changes.

Example: Fire can warm up a cold and when hot breath in the body due to exercise so that the body becomes cold expelled.

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2. Temperature changes occur

In a chemical reaction, reactants are converted into products. Changes may occur due to the termination of ties antaratom reagents and formation of new bonds that make up the product. Energy required to break the tie.

A chemical reaction occurs in a space that we call dbngan system, places outside the system is called the surroundings.

In exothermic reactions, heat transfer occurs from sisitem to the environment.

In endothermic reactions occur transfer heat energy from the environment to the system.

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3. Sediment formation occurs

When two solutions react in a test tube, sometimes forming an insoluble sneyawa, solid, and separated from the solution. The solid is called the precipitate (precipitate)

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4. Gas Formation occurs

Simply put, the chemical reaction created a gas which indicated the presence of bubbles in solution reacted. The gas can be determined from the typical smell, like sour sulfide (H2S) and ammonia (NH3), which stinks.