About Stoichiometry

STOICHIOMETRY
The word stoichiometry is derived from the Greek words stoicheion, which means element, and metrein, which means to measure. The numerals used to balance a chemical equaton are known as stoichiometric coefficients. These numbers are essential for solving problems based on chemical equations. Hece such problems are also called stoichiometric calculations.
For stoichiometric calculations, the mole relationships between different reactants and products are required, as from them, the mass-mass, mass-volume and volume-volume relationships between different reactants and products can be obtained.
Concept of Limiting Reagent
In single-reactions, the calculations are carried out wi only that amount of teh reactant which has converted to the product. This is done in all the methods mentioned above.
In the reactions where more than one reactant is involved, one has to first identify the limiting reactant, i.e., the reactant which is completely consumed. All calculations are to be carried out with the amount of the limiting reactant only. Now the questioni s how to identify the limiting reactant? The procedure is simple as illustrated below:
Initially.... 5 moles 12 moles 0 moles
A + 2B ----> 4C
If A is the limiting reactant : moles of C producec = 20
If B is the limiting reactant : moles of C produced = 24
The reactant producing the least number of moles of the product is the limiting reactant and hence A is the limiting reactant. Thus,
Initially .... 5 moles 12 moles 0 moles
A + B -------> 4C
Finally.... 0 moles 2 moles 20 moles
The limiting reactant can also be ascertained by knowing the initial number of equivalents of each reactant. The reactant with the least number of equivalents is the limiting reactant. The equivalent method to identify the limiting reactant can be applid even if the chemical equation is not balanced.