According to Van't Hoff , lnK = A-∆H RT , where A is a constant, ∆H is the denaturation enthalpy, R is the universal gas constant and T is the absolute temperature. When DNA has reached 50% denaturation, or the equilibrium constant K = 1, we have the constant term A = ( ∆H RT ) T m and the Van't Hoff equation has the following form: