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|It is a unit of||Amount of Substance|
|Unit System||SI base Unit|
Mole is defined as the amount of a substance containing as many atoms, molecules, ions, electrons or other elementary entities as there are carbon atoms in exactly 12 gram of 12C. Chemists have defined the mole as a 'definite number'. This definite number is called the Avogadro constant, equal to 6.02 × 1023 particles and 22.4 liters. Mole is denoted by mol.
The mole is widely used in chemistry instead of units of mass or volume as a convenient way to express amounts of reactants or of products of chemical reactions. For example, the chemical equation 2 H2 + O2 → 2 H2O implies that 2 moles of dihydrogen (H2) and 1 mole of dioxygen (O2) react to form 2 moles of water (H2O). The mole may also be used to express the number of atoms, ions, or other elementary entities in a given sample of any substance. The concentration of a solution is commonly expressed by its molarity, defined as the number of moles of the dissolved substance per litre of solution.
The term gram-molecule was formerly used for essentially the same concept. The term gram-atom (abbreviated gat has been used for a related but distinct concept, namely a quantity of a substance that contains Avogadro's number of atoms, whether isolated or combined in molecules. Thus, for example, 1 mole of MgB2 is 1 gram-molecule of MgB2 but 3 gram-atoms of MgB2.
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