Define equilibrium constant. Write the equilibrium constant expression for the reaction of ${\mathrm{H}}_2\left(\mathrm{g}\right)+{\mathrm{I}}_2\left(\mathrm{g}\right)\rightleftharpoons 2\mathrm{HI}\left(\mathrm{g}\right)$ and its reverse reaction. How are the two equilibrium constants related.

State law of chemical equilibrium? What is ${\mathrm{K}}_{\mathrm{c}}$ for the following equilibrium when the equilibrium concentration of each substance is: $\left[\mathrm{S}{\mathrm{O}}_2\right]=0.60\mathrm{M}, \left[{\mathrm{O}}_2\right]=0.82\mathrm{M} \mathrm{a}\mathrm{n}\mathrm{d}\left[\mathrm{S}{\mathrm{O}}_3\right]=1.90\mathrm{M} ?$

$2\mathrm{S}{\mathrm{O}}_2\left(\mathrm{g}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)\rightleftharpoons 2\mathrm{S}{\mathrm{O}}_3\left(\mathrm{g}\right)$

Explain the significance of a very large value of $\mathrm{K}$.

Explain the significance of a very small value of $\mathrm{K}$.

Explain the significance of 

c) a value of $\mathrm{K}$ about $1.0$

Why is it useful to compare $\mathrm{Q}$with $\mathrm{K}$?