Stoichiometry is the study and calculate the quantitative relationships of the reactants and products in chemical reactions (chemical equations). The word is derived from the Greek stoikheion (elements) and metriā (size).
Determination of the reaction stoichiometry is the mass ratio of the elements in a compound in the formation of compounds. In the calculation of chemical stoichiometry, usually required fundamental laws of chemistry. basic laws of chemistry, the law of conservation of mass, the law of comparative fixed, and multiple comparative law.
Stoichiometric gas is a particular form, in which the reactants and products entirely in the form of gas. In this case, the coefficient of substance (mole ratio stating the reaction stoichiometry) also has stated volume ratio between the substances involved.

a. The initial phase of stoichiometric
At the beginning of chemistry, quantitative aspects of chemical change, the chemical reaction stoichiometry, did not get much attention. Even when attention has been given, experimental techniques and tools do not produce correct results.
One example involves the theory of phlogiston. Flogistonis tried to explain the phenomenon of combustion with the term “flammable substance”. According to the flogitonis, combustion is a release of flammable substances (from the burning substance). This substance was later called “phlogiston”. Based on this theory, they defined as the release of phlogiston combustion of flammable substances. Mass changes when burning wood fits well with this theory. However, the change in mass of metal when calcined does not match the theory. However flogistonis accept that the two processes are essentially identical. Increasing the mass of calcined metal is a fact. Flogistonis tried to explain this anomaly by stating that phlogiston negative mass.
Philosophers of Flanders January Baptista van Helmont (1579-1644) experimented “willow” famous. He is growing seedlings of willow after measuring the mass of flower pots and soil. Since there is no mass change flower pots and soil when the seed grows, it assumes that the masses were obtained only because of water coming into the ore. He concludes that “the root of all matter is water”. Based on the current outlook, hypothesis and experiment are far from perfect, but the theory is a good example of the attitude of the quantitative aspects of chemistry that are growing. Helmont recognize the importance of stoichiometry, and clearly ahead of his time.
In the late 18th century, German chemist Jeremias Benjamin Richter (1762-1807) invented the concept of equivalent (in terms of modern chemistry chemical equivalent) with a reaction carefully acid / base, the quantitative relationship between acids and bases in the neutralization reaction. Equivalent Richter, or what is now called the chemical equivalent, indicating a certain amount of material in the reaction. The neutralization equivalent in regard to the relationship between the number of acid and a base for mentralkannya. Proper knowledge is essential to produce the equivalent of soap and gunpowder good. Thus, such knowledge is very important in practice.

At the same time Lavoisier established the law of conservation of mass, and provide a basis equivalent to the concept of an accurate and creative experiments. Thus, the stoichiometry handle the quantitative aspects of chemical reactions into chemical basic methodology. All the fundamental laws of chemistry, of the law of conservation of mass, the law of comparative law remains until all based gas reaction stoichiometry. Fundamental laws are the basis of the atomic theory, and consistently explained by atomic theory. However, it is interesting to note that the concept of equivalent used before atomic theory was introduced.

b. The relative atomic mass and atomic mass
Dalton recognized that it is important to determine the mass of each atom as mass varies for each type of atom. Atom is very small so it is not possible to determine the mass of a single atom. So he focuses on the relative masses and create a table atomic mass (Figure 1.3) for the first time in human history. In the table, the mass of the lightest element, hydrogen adoption as a standard one (H = 1). Atomic mass is a relative value, meaning that a dimensionless ratio. Although several different atomic masses with modern values, most of the proposed values ​​in the range of compatibility with the current value. This shows that the idea and the experiment right.
Then the Swedish chemist Jons Jakob Berzelius Baron (1779-1848) to determine the mass of the oxygen atom as the standard (O = 100). Because Berzelius get this value based on the analysis of oxide, it has a clear reason to choose oxygen as standard. However, the standard hydrogen is clearly superior in terms of simplicity. Now, after much discussion and modification, carbon standard is used. In this method, the mass of 12C carbon with 6 protons and 6 neutrons is defined as 12.0000. Atomic mass is the mass of an atom relative to this standard. Although carbon has been declared as standard, this can actually be considered as a standard hydrogen is modified.
Atomic mass of almost all the elements very close to integers, ie integer multiples of hydrogen atomic mass. This is a natural kosekuensi fact that the hydrogen atom mass equal to the mass of a proton, which in turn is almost equal to the mass of a neutron, and electron mass is very small to negligible. However, most of the naturally occurring element that is a mixture of several isotopes, and atomic mass depends on the distribution of isotopes. For example, the atomic mass of hydrogen and oxygen is 1.00704 and 15.9994. The mass of the oxygen atom is very close to the value of 16 is a bit smaller.

Molecular mass and formula mass
Each compound is defined enumerated by a chemical formula that indicates the type and number of atoms that make up compound. The mass formula (or formula mass) is defined as the sum of the atomic masses based on the type and number of atoms in the chemical formula defined. The chemical formula of molecules called molecular formula, chemical formula and mass is called the mass molekul.5 example, the molecular formula of carbon dioxide is CO2, and the molecular mass is 12 + (2x 6) = 44. As the mass of the atom, both mass and molecular mass formula should not be an integer. For example, the molecular mass of hydrogen chloride HCl is 36.5. Even if the type and number of atoms that make up molecules are identical, the two molecules may have different molecular masses when there are different isostop involved.
It is impossible to define molecules for compounds such as sodium chloride. Mass formula for sodium chloride is used instead of molecular mass.

c. Quantity of matter and mole
Quantitative methods most suited to express the amount of matter is the number of particles such as atoms, molecules that make up the material being discussed. However, to calculate the atomic or molecular particles are very small and can not be seen very difficult. Instead of counting the number of particles is directly the number of particles, we can use the mass of a certain number of particles. Then, how does a certain amount of numbers chosen? For
long story short, the number of particles in a 22.4 L of gas at STP (0 ℃, 1ATM) was selected as the standard amount. This number is called Avogadro’s number. Name number Loschmidt also proposed to honor the Austrian chemist Joseph Loschmidt (1821-1895) who first with the experiment (1865).
Since 1962, according to the SI (Systeme Internationale) decided bahwam in the world of chemistry, mole is used as a unit of the amount of matter. Defined Avogadro’s number of carbon atoms in 12 g 126C and renamed Avogadro constant.
There are several definitions of “mole”:
(I) The amount of material that contains a number of particles contained in 12 g of 12C. (Ii) one mole of material that contains Avogadro constant number of particles.
(Iii) A material that contains 6.02 x 1023 particles in one mole.
d. Atomic mass units (sma)
Because the standard atomic mass is the mass of hydrogen Dalton system, standard mass in the right SI 1/12 the mass of 12C. This value is called the atomic mass unit (sma) and is equal to 1.6605402 x 10-27 kg, and D (Dalton) is used as a symbol. Atomic mass is defined as the ratio of the average sma elements with natural isotopic distribution with 1/12 sma 12C.

Chemical law is a law of nature that are relevant to the field of chemistry. The most fundamental concept in chemistry is the law of conservation of mass, which states that no changes in the quantity of matter during an ordinary chemical reaction.
Additional law in chemistry to develop the law of conservation of mass. Comparative law remains of Joseph Proust states that pure chemicals are composed of elements with a certain formula we now know that the structural arrangement of these elements are also important.
Multiple comparisons law of John Dalton stated that the chemicals will be present in the form of the proportion of small integers (eg 1:2; O: H in water = H2O), although in many systems (especially Biomacromolecules and minerals) this ratio tends require large numbers, and is often given in the form of fractions. Such compounds are known as non-stoikhiometrik compounds.

Another modern chemical law to determine the relationship between energy and transformation.
a. In equilibrium, a molecule found in the mixture is determined by the transformations that may occur on a time scale equilibrium, and has a ratio determined by the intrinsic energy of the molecule. The smaller the intrinsic energy, the more molecules.
b. Change one structure into another structure requires the input of energy to overcome the energy barrier: this can be caused by intrinsic energy molecule itself, or from external sources will generally accelerate the change. The greater the energy barrier, the slower the process of ongoing transformation.
c. There is a structure or a transition between the hypothetical, which relates to the structure at the top of the energy barrier. Hammond Postulate-Leffer stated that this structure resembles origin products or materials that have intrinsic energy closest to the energy barrier. By stabilizing the hypothetical structure with the chemical interaction is one way to achieve catalysis.
d. All chemical processes are irreversible (reversible) (microscopic keterbalikkan legal) process has a bias although some energy, they basically takterbalikkan (irreversible).