According to law of conservation of mass, in a chemical reaction mass can neither be destroyed nor created thus, the total mass created here will be 224 g+28 g=252 g thus, mass of involved should be 252 g.
This can be experimentally proved as follows:
The balanced chemical reaction for the above process will be as follows:
Considering any one of the reactant.
2 mol of are produced from 2 mol of
thus, 1 mol of
produced from 1 mol of
.
Now, mass of hydrogen gas is 28.0 g, molar mass is 2 g/mol, converting mass into number of moles:
thus, 14 mol of produced from 1×14=14 mol of
.
Molar mass of is 18 g/mol. Converting number of moles into mass as follows:
m=n×M=14 mol×18 g/mol=252 g
Thus, mass of involved in the reaction will be 252 g.