4

a)
c\left(HI\right)=\frac{1{,}00mol}{5{,}00l}=0{,}20\ \frac{mol}{dm^3}
\begin{array}{l|l} &HI&H_2&I_2\\ \hline c_{alku}&0{,}20&&\\ muutos&-2x&+x&+x\\ c_{tasap}&&& \end{array}
K_c=0{,}015=\frac{\left[H_2\right]\left[I_2\right]}{\left[HI\right]^2}=\frac{x^2}{\left(0{,}20-2x\right)^2}
x=0{,}019675
\left[HI\right]=0{,}20\ \frac{mol}{l}-2\cdot0{,}019675\ \frac{mol}{l}=0{,}16065\ \frac{mol}{l}
n\left(HI\right)=5l\cdot0{,}16065\ \frac{mol}{l}=0{,}80\ mol