m tăng= m kim loại - mH2
\(m_{H2}=0,8\left(g\right)\)
\(\Rightarrow n_{H2}=0,4\left(mol\right)\)
Gọi a là mol Mg, b là mol Fe
\(\Rightarrow24a+56b=12,8\left(1\right)\)
Bảo toàn e: \(2a+2b=0,4.2=0,8\left(2\right)\)
\(\left(1\right)+\left(2\right)\Rightarrow\left\{{}\begin{matrix}a=0,3\left(mol\right)\\b=0,1\left(mol\right)\end{matrix}\right.\)