NCERT Chemistry class 11 - Online Notes : Stoichiometry

Here, we will discuss Stoichiometry from unit 1 of CBSE Class 11 Chemistry.

What is stoichiometry?

The relationship between the relative quantities of substances taking part in a chemical reaction or forming compounds, typically a ratio of whole integers.

Mole: The mole is the SI unit for the amount of substance. In short, it is written as “mol”. Mole is defined as the amount of a substance that contains the same number of entities (electrons, atoms, ions, or molecules) as the number of atoms in 12 grams of carbon-12 (12C). This is given by Avogadro’s number, in honor of an Italian physicist Amedeo Avogadro.

Avogadro number gives the number of units in one mole of any substance, which is equal to 6.0221×1023.The units may be electrons, atoms, ions or molecules depending on the nature of the substance and the reaction it undergoes. This means that one mole contains 6.023×1023 entities/units.

The importance of the mole unit is:

The mole unit allows us to relate the number of entities to the mass of a sample of those entities. For example; 1mol of 12C contains 6.022×1023 carbon-12 atoms and has a mass of 12 grams. This means that by the use of mole unit, we can count the number of entities by weighing the sample. If we find the weight of the sample of 12C to be 6 grams (g), so it means the sample of carbon-12 is 0.5 mol and it contains 3.011×1023
The mole maintains the same numerical relationship between mass on the atomic scale (atomic mass units, amu) and mass on a macroscopic scale (grams, g). This relationship is same for the elements as well as for the compounds. As explained here:

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