Stoichiometry Formula

The word stoichiometry is originated from the Greek word stoicheion meaning elementary constituent, and metrin relates to measuring. Stoichiometry involves quantitative calculations of reactants and products in chemical reactions. It’s based on the law of conservation of mass where the total mass of reactants is equal to the total mass of the products. Stoichiometry is founded on the law of conservation of mass where the total mass of the reactants = total mass of the products.  The amount of product can easily be calculated if the amounts of the separate reactants are known. 

CH4 + 2 O2 → CO2 + 2 H2O

Here, One molecule of methane (CH4) reacts with 2 molecules of Oxygen gas to achieve 2 molecules of CO2 and two molecules of water. The quantitative relationship here is measured by the Stoichiometry and also used to find out the amount of reactants that are yield in a given reaction.
Solved Examples 
Example 1  Ammonia reacts with solid copper oxide and releases nitrogen gas, solid copper and water vapour. Write this chemical reaction and balance the equation according to its stoichiometry.
Solution:   The above example can be written as
NH3 + CuO —> Cu + H2O + N2
Balanced equation based on its stoichiometry,
2NH3 + 3CuO —> 3Cu + 3H2O + N2Example 2 Sulphur trioxide gas is released on combustion of iron pyrites(FeS2). Describe the chemical reaction and balance the equation based on the stoichiometry of every compound.
Solution: The chemical reaction for the above example is
FeS2 + O2 —> Fe2O3 + SO3
Combustion compounds react with oxygen.
The balanced chemical equation based on its stoichiometry is
4FeS2 + 15O2 —> 2Fe2O3 + 8SO3

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