How equilibrium constant determine whether its strong or weak acid?
strong acid is 100% dissociated, so in the expression for the equilibrium constant [products]/[reactants], the denominator will be essentially zero, and the numerator equal to the molar concentration of the acid itself. Consequently, the equilibrium constant will be very large for a strong acid. In your example, 10^9 is pretty big, and 10^-4 is very small. as a rule of thumb when discussing equilibria, > 10^3 is considered large and < 10^-3 is considered small.
