Summary:
- The entropy of a pure crystalline substance at absolute zero is defined to be equal to zero.
- As the temperature of the substance increases, its entropy increases because of an increase in molecular motion.
- The entropy change for a reaction can be determined if the standard entropies of each substance are known.
- The units for entropy are J/K • mol.
- Standard entropie for a few substances are shown in the Table below:Standard Entropy Values at 25°C.
- The symbol for entropy is and the standard entropy of is given by the symbol , indicating that thestandard entropy is determined under standard conditions.