Читать книгу Open and Toroidal Electrophoresis - Tarso B. Ledur Kist - Страница 13

The temperature of a solvent, for instance water, acetonitrile or methanol, is related to the average energy per degree of freedom that these molecules have. Average energy is given by , where represents the Boltzmann constant and represents temperature in Kelvin.[1] The degrees of freedom consist of the translation velocity, which occurs in the three space coordinates, and both the vibrational and rotational degrees of freedom of the molecules. Raising the temperature of liquid water at 1 atm from 278.15 K (5 C or 41 F) to 348.15 K (75 C or 167 F) increases the average velocity (), indeed , by about 25%. The consequential increase in thermal energy is important for the collision rate and momentum transfer among the molecules within the liquid. Such collisions with fast-moving molecules cause random movements of the microscopic particles that are suspended in the liquid (or in a gas), which can be observed under the microscope (Brownian motion). This is the basis for the denaturation and renaturation of nucleic acids, as well as the denaturation of proteins (disruption of both the secondary and tertiary structures). This same process also plays a role in dissolution, dissociation, ionization, and in maintaining the equilibrium of reactions. The Gibbs free energy change quantitatively gives the role of enthalpy, temperature and entropy for chemical reactions in the general case (see Section 1.1.8).