\(n_{N_2}=\dfrac{3,5}{28}=0,125\left(mol\right)\\
n_{O_2}=\dfrac{0,56}{22,4}=0,025\left(mol\right)\\
pthh:N_2+O_2\underrightarrow{t^o}2NO\\
LTL:\dfrac{0,125}{1}>\dfrac{0,025}{1}\)
=> N2 dư
\(n_{N_2\left(p\text{ư}\right)}=n_{O_2}=0,025\left(mol\right)\\
m_{N_2\left(d\right)}=\left(0,125-0,025\right).28=2,8\left(g\right)\\
n_{NO}=2n_{O_2}=0,5\left(mol\right)\\
m_{NO}=0,5.30=15\left(g\right)\\
m_{sp}=2,8+15=17,8\left(g\right)\)