# In which area is stoechiometry used

## Stoichiometry

Stoichiometry, the doctrine of the calculation of the composition chem. Compounds and mixtures as well as the mass, volume and charge ratios in chem. Reactions. The development of the S. was an important prerequisite for the development of chemistry into an exact science.

The S. is based on the established experience that with chem. Reactions that chem. Elements are completely preserved (Law of Conservation of the Elements) and the total mass of the substances involved is constant (Law of Conservation of Mass). The actual stoichiometric laws include the laws of stoich. Proportions, Gay-Lussac's chemical law of volume. and Avogadro's Law. The basis for the S. of electrochem. Processes form Faraday's laws, to stöch. To calculate reactions in which gases are involved, the equation of state of ideal gases is required.

Applications. The application of the S. to mixtures or solutions includes dealing with composition quantities. The implementation stoch. Calculations are required in almost all areas of chemistry. The following use cases are the most common.

1) S. the composition of compounds. The basis here is the size of the mass m, molar mass M. and amount of substance n linking equation M. = m/n and the finding that the stoichiometric numbers νi Specify molar ratios in a formula. So z. B. for Fe2O3nFe : nO = νFe : νO = 2: 3. Typical tasks are the calculation of the mass fractions w of the individual elements in a compound from the substance formula or the determination of the substance formula from the experimentally determined mass fractions of the elements (elemental analysis).

2) S. of chemical reactions. The calculation of the metabolic rate at chem. Reactions are based on the corresponding reaction equation (material equation), which the Describes the relationships between the starting and end materials. The equation N2 + 3 H.2 → 2 NH3 gives for the molecular domain the elementary formula turnover (Reaction from an N2Molecule with three H.2-Molecules to two NH3Molecules) and at the same time presses for the macroscopic material area molar formula conversion (1 mol = 28.0 g N2 reacts with 3 mol = 6.0 g of H2 to 2 mol = 34.0 g of NH3) out. About the relationship m = nM the quantities of substances can be converted into masses.

As yield of a reaction is the quotient of the practically obtained and the theoretically possible amount of end product (s) (i.e. when the reaction is complete according to its S.