Thursday, August 11, 2011

Units of Entropy

The unit of entropy depends upon the unit of heat employed and the absolute temperature. We know that
                                                           Change in entropy (dS) = &Q/T
       Therefore, if the heat supplied or rejected is in kJ and the temperature is in K, then the unit of entropy is kJ/K. The entropy may be expressed in so many units entropy without assigning any dimensional units. Since the entropy is expressed per unit mass of the working substance, it would be more correct to speak specific entropy. The absolute values of entropy cannot be determined, but only the change in entropy may be obtained by using equation.
     Theoretically, the entropy of a substance is zero at absolute zero temperature. Hence, in entropy calculation, some convenient datum should be selected from which measurement may be made.
        It may be noted that water 0degree C is assumed to have zero entropy, and changes in its entropy are reckoned from this temperature.

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