The thermal denaturation process involves breaking DNA bonds with dominant Van der Waals forces of an enthalpic nature. We have the enthalpy-dominated hydrogen bond limiting denaturation in the case of DNA chemical denaturation at experimental conditions of authors. Changes in DNA type and/or length and conditions of the experiment might lead to energetically different limiting steps in the chemical denaturation process related to The melting temperature for thermal denaturation is lower than chemical: 7-8 • K for T4 bacteriophage DNA.