The mole concept

Amount in moles (n) is a important quantity in chemical calculations as the same amount in moles of two substances contain the same number of formula units of those substances.
 
In 1 mol NaCl the number of NaCl units equals the number of C6H12O6 units in 1 mol C6H12O6.

The number of particles in one mole has been determined experimentally to be 6.022 × 1023. The Avogadro constant (
) is equal to 6.022 × 1023 mol–1.

The coefficients in the balanced equation for a reaction give the ratio of
  • the number of formula units of reactants required for complete reaction to
  • the number of formula units of products formed.
     
    2H2 + O2 2H2O
    2 molecules of H2 plus 1 molecule of O2 gives 2 molecules of H2O
    2 moles of H2 plus 1 mole of O2 gives 2 moles of H2O

Thus the coefficients also give the ratio of
  • amounts in moles of reactants required for complete reaction.
  • amounts in moles of products formed to the amount in moles of reactants used.