\(n_{Al}=\dfrac{10,8}{27}=0,4\left(mol\right)\)
PT: \(2Al+3S\underrightarrow{t^o}Al_2S_3\)
Theo PT: \(n_{Al_2S_3\left(LT\right)}=\dfrac{1}{2}n_{Al}=0,2\left(mol\right)\)
\(\Rightarrow m_{Al_2S_3\left(LT\right)}=0,2.150=30\left(g\right)\)
\(\Rightarrow H=\dfrac{25,5}{30}.100\%=85\%\)