Calculations of Reacting Masses

A balanced equation gives the reacting ratio of moles of reactants and products or stoichiometry of a reaction. In a reaction, mass is conserved.
In the reaction4 Al (s) + 3 O₂ (g) → 2 Al₂O₃ (s)
4 moles of aluminium will react with 3 moles of oxygen gas to form 2 moles of aluminium oxide.The number of moles = mass (in g) ÷ molar mass (in g mol^-1, numerically equal to M_r).

n

=

Mass   Mr

Given:mass = moles × M_r4 moles of aluminium =(27 x 4) =108g3 moles of oxygen =(32 x 3) =96g2 moles of aluminium oxide = (102x 2) =204g