Abstract: The enthalpy change of formation reaction of the N-phenyl-N′-(1,2,3-thiadiazol-5-yl)urea has been determined by a microcalorimeter, using 5-amino-1,2,3-thiadiazole and phenylisocyanate as starting materials in the solvent of THF. The reaction temperature was kept at 25 ℃. On the basis of experimental and calculated results, the enthalpy change is Δ_rH_m^o=(-142.304±0.390) kJ·mol^-1; the reaction order is n=1/2; the rate constant k=1.3579×10^-4 s^-1 and the activation free-energy is ΔG_m^o=95.098 kJ·mol^-1. The result indicates that the title reaction takes place easily at room temperature.

Key words: N-Phenyl, N′-(1,2,3-thiadiazol-5-yl)urea, Formation reaction, Thermochemical property