a) \(N_2+O_2\rightarrow2NO\)

\(\begin{matrix}N^0\rightarrow N^{+2}+2e\\O^0+2e\rightarrow O^{-2}\end{matrix}|\begin{matrix}\times1\\\times1\end{matrix}\)

b) \(C_2H_5OH+3O_2\rightarrow2CO_2+3H_2O\)

\(\begin{matrix}C^{-2}\rightarrow C^{+4}+6e\\O^0+2e\rightarrow O^{-2}\end{matrix}|\begin{matrix}\times1\\\times3\end{matrix}\)

c) \(CH_4+2O_2\rightarrow CO_2+2H_2O\)

\(\begin{matrix}C^{-4}\rightarrow C^{+4}+8e\\O^0+2e\rightarrow O^{-2}\end{matrix}|\begin{matrix}\times1\\\times4\end{matrix}\)

d) \(2H_2S+3O_2\rightarrow2H_2O+2SO_2\)

\(\begin{matrix}S^{-2}\rightarrow S^{+4}+6e\\O^0+2e\rightarrow O^{-2}\end{matrix}|\begin{matrix}\times1\\\times3\end{matrix}\)

e) \(4NH_3+3O_2\rightarrow2N_2+6H_2O\)

\(\begin{matrix}N^{-3}\rightarrow N^0+3e\\O^0+2e\rightarrow O^{-2}\end{matrix}|\begin{matrix}\times2\\\times3\end{matrix}\)

Sô kg gạo đã dùng là :

\(32\times\dfrac{1}{8}=4\) (kg)

Còn lại số kg gạo là :

\(32-4=28\) (kg)

Đ/s : 28 kg