-calculez moli Mg
6,023x10²³atomi.(nr.Avogadro)........1molMg
18,069x10²³atomi..............................n= 3mol
-ecuatia reactiei
1mol 1mol
Mg + Cl2---> MgCl2
n=...............2,5mol
pentru ca n= 2,5mol Mg rezulta ca 3-2,5 mol Mg este in exces si nu intra in reactie