The enthalpy of the second stage of chemical denaturation (formation of new bonds with components of surrounding solution) is ∆H exo . This process occurs spontaneously because the energy of interaction between active sites of DNA and components of the surrounding solution (including possible renaturation) should be higher or at least equal to the energy of initial inter-DNA bonding involved in the denaturation process or ∆H exo ≥ ∆H endo . (See Eq. 12) Thus, chemical denaturation is an exothermic process, negatively affecting the net enthalpy.