Which statement is always true for a chemical reaction that has reached equilibrium?

Deduce the equilibrium constant expression for the following homogeneous equilibrium reaction.

$\frac{1}{2}{\mathrm{N}}_2\left(\mathrm{g}\right)+\frac{3}{2}{\mathrm{H}}_2\left(\mathrm{g}\right)\rightleftharpoons {\mathrm{NH}}_3\left(\mathrm{g}\right)$

Deduce the equilibrium constant expression for the following homogeneous equilibrium reaction.

$\mathrm{ClN}{\mathrm{O}}_2\left(\mathrm{g}\right)+\mathrm{NO}\left(\mathrm{g}\right)\rightleftharpoons {\mathrm{NO}}_2\left(\mathrm{g}\right)+\mathrm{ClNO}\left(\mathrm{g}\right)$

Deduce the equilibrium constant expression for the following homogeneous equilibrium reaction.

$4{\mathrm{NH}}_3+5{\mathrm{O}}_2\rightleftharpoons 4\mathrm{NO}\left(\mathrm{g}\right)+6{\mathrm{H}}_2\mathrm{O}\left(\mathrm{g}\right)$ 

The equilibrium constant for the reaction between hydrogen and chlorine gas to produce hydrogen chloride gas is $2.40\times {10}^{33}$ at $298 \mathrm{K}$.

 ${\mathrm{H}}_2\left(\mathrm{g}\right)+{\mathrm{Cl}}_2\left(\mathrm{g}\right)\rightleftharpoons 2\mathrm{HCl}\left(\mathrm{g}\right)$

Calculate the equilibrium constant for the reverse reaction, namely the decomposition of $\mathrm{HCl}$.

The equilibrium constant for the equilibrium between ${\mathrm{N}}_2{\mathrm{O}}_4$ and ${\mathrm{NO}}_2$ is $7.7\times {10}^{-4}$ at $273 \mathrm{K}$.

 ${\mathrm{N}}_2{\mathrm{O}}_4\left(\mathrm{g}\right)\rightleftharpoons 2{\mathrm{NO}}_2\left(\mathrm{g}\right)$

Calculate the equilibrium constant for

 $\frac{1}{2}{\mathrm{N}}_2{\mathrm{O}}_4\left(\mathrm{g}\right)\rightleftharpoons {\mathrm{NO}}_2\left(\mathrm{g}\right)$  at $273 \mathrm{K}$.

${\mathrm{PCl}}_5\left(\mathrm{g}\right)\rightleftharpoons {\mathrm{PCl}}_3\left(\mathrm{g}\right)+{\mathrm{Cl}}_2\left(\mathrm{g}\right); \mathrm{\Delta H}º=+92.5 \mathrm{kJ}$ 

Predict and explain any shift in the equilibrium position when the temperature of the system is decreased.

${\mathrm{PCl}}_5\left(\mathrm{g}\right)\rightleftharpoons {\mathrm{PCl}}_3\left(\mathrm{g}\right)+{\mathrm{Cl}}_2\left(\mathrm{g}\right) \mathrm{\Delta H}º=+92.5 \mathrm{kJ}$ 

Predict and explain any shift in the equilibrium position when an additional chlorine gas is injected into the system.