We know that the chemical equation gives us the quantitative relationship between the reactants and the products. This quantitative information can be utilised to carry out variety of calculations which are required many a times, to assess · the economic viability of the chemical process. calculations based on the quantitative relationship between the reactants and the products are also referred to as stoichiometry. The term stoichiometry is derived from Greek words Stoicheion meaning element and metron meaning measure. Stoichiometry is, therefore, that area of chemistry and chemical technology on which determination of quantities of reactants and products of chemical reaction is based.
CALCULATIONS OF QUANTITIES OF SUBSTANCES IN CHEMICAL REACTIONS
A balanced equation indicates the mole ratio of substances involved in the reaction. Quantities of substances can be an amount of substance in mol, mass in g or kg, volume in cm3 or dm3, concentration in mol dm-3 or g dm-3, or number of particles.
The mole ratio can be used to calculate unknown quantities given known quantities of reactants or products. Such calculations are done in industry on a large scale to find the maximum theoretical yield of product from a given mass of reactant. Such calculations have important economic implications.
In order to solve the problems based on chemical calculations the following steps, in general, are quite helpful.
(i) Write the balanced chemical equation.
(ii) From the chemical equation write the molar ratio between the given and required substance.
(iii) Convert these moles into the desired parameters such as mass or volume.
(iv) Calculate the final result by applying unitary method.
Reading Chemical Equations
Chemical equations can· be interpreted in many ways i.e., number of entities, amount of substance, mass of substance, concentration, volume of substance, percentage yield of products etc. The idea is illustrated by following example:
Mg (s) + 2HCl (g) à MgCl2 + H2(g)