In the present investigation the aim was not only to extend the temperature range but also to obtain data of a higher order of accuracy than that previously reported. The heat capacity must be zero at zero temperature in order for the above integral not to yield an infinite absolute entropy, thus violating the third law of thermodynamics. Furthermore, in the previous work the possibility that rubber at low temperatures might exist either as a metastable amorphous form or as a crystalline form was not clearly recognized. Several investigators have previously determined the heat capacities of rubber, but their observations were not made at temperatures sufficiently low to permit accurate extrapolation to the absolute zero in order to apply the third law. Then from this latter value, along with the entropy values of carbon (graphite) and gaseous hydrogen and the heat of formation of rubber, a reliable value for the free energy of formation of rubber may be calculated. From these heat-capacity values the entropy may be obtained. The symbol c stands for specific heat and depends on the material and phase. where Q is the symbol for heat transfer, m is the mass of the substance, and T is the change in temperature. This makes necessary the determination of heat-capacity values of rubber from room temperature down to temperatures sufficiently low to apply an empirical formula for obtaining the values below this lower temperature. Combining the heat capacity data with the enthalpy data on phase transformations, the absolute entropy of a substance, whether solid, liquid or gas, at. The quantitative relationship between heat transfer and temperature change contains all three factors: Q mc T, 14.2. It AS0 Absolute entropies of products and Reactants in Solide are. The best method for obtaining the free energy of formation of rubber is by making use of the third law of thermodynamics. Suggests at absolute zero, all substances have same heat capacities.
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