1mol 1mol
H2+ CuO===> Cu +H2O
x.............7mo
x= calculeaza
2,H2 +_ Cl2---> 2HCl
2g............2x35,5g
24g.........................m= 852g Cl2;dar avem doar 568g Cl2 ,deci H2 este in exces
2gH2..........2x35,5gCl2
x.........................568g
x=m,H2=16g---------------> excesul H2=24-16 g