The hydration reaction of sulfuric acid is highly exothermic, dilution.
As indicated by its acid dissociation constant, sulfuric acid is a strong acid:
: K = 1000 (pK = −3)
The product of this ionization is , the bisulfate anion.  Bisulfate is a far weaker acid:
: K = 0.01 (pK = 2) 
The product of this second dissociation is , the sulfate anion.