Calorimetric Stusy of Cadmium(II) and Lead(II) Complexes with Thiourea

Department of Chemistry, Regional Engineering College, Durgapur-713

University Department of Chemical Technology, Bombay-400 019

Manuscript received 24 December 1982, revised 27 February 1984, accepted 3 May 1984

Precise calorimetric measurements of the Cd^II-thiourea and Pb^II-thiourea systems in 1 M NaCIO₄ solution were made using a thermistor as the temperature measuring device in the system, and the values of the stepwise and overall changes in\(\bigtriangleup\)G^o,\(\bigtriangleup\)H^o and \(\bigtriangleup\)S^o accompanying the complex formation reactions were evaluated. Values of the overall enthalpy (\(\bigtriangleup H^o_n\)) and entropy (\(\bigtriangleup S^o_n\)) changes for the mono-, bis-, tris- and tetrakis-coordinated species are for Cd_II ion -10.75 and -7.7, -34.04 and -63.5, -20.81 and -17.8, -43.35 and -66.5, respectively; while for Pb^II ion -12.25 and -28.4, -19.16 and -57.4, -10.61 and -19.4, -39.80 and -84.8, respectively at 30^o with \(\mu\)= 1.0.