An automatic adiabatic colorimeter was used to measure the heat capacity at 220--320 K for the H2O/NaY zeolite adsorption system with various amts. of adsorbed water. The results obtained from CP- T measurements show that there is no peak for the solid-liq. phase transition of adsorbed water. This means that no aggregate state of water is formed on the surface under these conditions and no solid-liq. phase transition can occur. Heat capacity measurements for H2O/NaY zeolite systems were made on samples prepared by mixing mech. the saturated H2O/NaY adsorption system with fixed amts. of water. There are clear peaks on the CP-T curves. If the water mixed in the saturated adsorption system is evacuated at once, the peak for the phase transition on the CP-T curves disappears. These water mols. bind to the external surface of the NaY particles. Interaction of water mols. and zeolite lowers surface of the heat, temperature, and entropy of fusion for these adsorbed H2O mols. compared to bulk water. Water adsorbed on the solid surface differs from normal bulk water.

Key words: ADSORPTION, MOLECULAR SIEVE, SURFACE CHEMISTRY, SPECIFIC HEAT, THERMOCHEMISTRY, SUPERMOLECULAR STRUCTURE