1. Physical and chemical properties of solvent mixtures are important for understanding their thermodynamic behavior. One of the most important considerations is that these properties may provide information about molecular interactions. Excess molar volumes, viscosity deviations and excess molar Gibbs energy of activation of viscous flow in isobutyric acid + water binary mixtures from 302.15 K to 313.15 K [1]. were calculated from experimental density and viscosity data presented in previous work. Here these experimental values were used to test the applicability of the correlative reduced Redlich-Kister equation and the Herráez and Belda equations as well as their corresponding relative properties. Their correlation ability at different temperatures, and the use of appropriate numbers of parameters, is discussed for the case of limited experimental data. The relative functions are important to reduce the effect of temperature and, consequently, to reveal the effects of different factors and types of interactions [2]. Values of limiting excess partial molar thermodynamic properties at infinite dilution were deduced from different methods. In this system it was found that structural order is not much destroyed by the activation process, and consequently bonds are not so much broken between the associated molecules to form smaller clusters (IBA:8 W). Keywords: Key words: First Tunisian Chemical Society Conference on Coordination Chemistry 8-10 May 2015, Sol Azur Beach Hotel, Hammamet – Tunisia. ISTMT., Laboratoire de Biophysique et Technologies M é dicales. VISCOSITYMEASUREMENTS VISCOSITY MEASUREMENTS * The molar excess free enthalpy: * Redlich-Kister expression for a molar excess property: * Herráez equation: * Reduced Redlich-Kister expression for a molar excess property: Figure 7 : Variation of the logarithm of activity coefficient lng 1 of IBA (from Eqs. 25, 26 and 33) for IBA + W mixtures versus molar fraction x 1 in IBA at the temperatures: (●): 301.15K ; (○): 302.15K; (▲): 305.15K ; (∆): 308.15K ; (■): 311.15K ; (□): 313.15K and (♦): 315.15K. Figure 8 : Variation of the logarithm of activity coefficient lng 2 of W (Eqs. 25, 26 and 33) for IBA + W mixtures versus molar fraction x 1 in IBA at the temperatures: (●): 301.15K ; (○): 302.15K; (▲): 305.15K ; (∆): 308.15K ; (■): 311.15K ; (□): 313.15K and (♦): 315.15K. Figure 9 : Correlation between the ratio lng i /x j 2 (from Eqs. 35 and 36) in IBA (1) + W (2) mixtures at the temperature 308.15 K. Figure 4 Correlation between the partial molar quantities relative to the activation energies Ea i /(kJ·mol -1 ) and the logarithm of the entropic factors of Arrhenius –R·ln(As i /Pa·s) /(J·K -1 ·mol -1 ) for {isobutyric acid (1) + water (2)} mixtures over the temperature range (302.15 to 313.15) K. (●): Ea 1 (x 1 ) vs. –R·ln(As 1 ) and Ea 2 (x 1 ) vs. –R·ln(As 2 ). Figure 5 The excess partial molar enthalpy ( ) / kJ·mol -1 of activation of viscous flow of IBA (1) and W (2) respectively for the system of (IBA-W) mixtures versus mole fraction x 1 in the temperatures range (from 301.15 to 315.15) K. (●) : and (○) :. Figure 6 The excess partial molar entropy ( ) / J·mol -1 ·K -1 of activation of viscous flow of IBA (1) and W (2) respectively for the system of (IBA-W) mixtures versus mole fraction x 1 in the temperatures range (from 301.15 to 315.15) K. (●) : and (○) :. Figure 1 Correlation between the Arrhenius activation energy E a (kJ·mol -1 ) of viscosity and the logarithm of the entropic factor of Arrhenius – R·ln(As/Pa·s) / (J·K -1 ·mol -1 ) for isobutyric acid (1) + water (2) mixtures in the temperature range (302.15 to 313.15) K. (●): experimental data points; (––): linear least square fit of Eq. 3. Figure 2 Arrhenius activation energy Ea /(kJ·mol -1 ) and partial molar activation energies of viscosity (Eqs. 7,8) Ea i /(kJ·mol -1 ) for {isobutyric acid (1) + water (2)} mixtures as a function of the mole fraction of isobutyric acid (x 1 ) over the temperature range (302.15 to 313.15) K. (▲): Ea(x 1 ) ; (●): Ea 1 (x 1 ) and ; (○): Ea 2 (x 1 ). Figure 3 Correlation between the partial molar Arrhenius activation energies Ea 1 (x 1 ) and Ea 2 (x 1 ) for {isobutyric acid (1) + water (2)} mixtures over the temperature range (302.15 to 313.15) K. [1] D. Das*, H. Salhi, M. Dallel, Z. Trabelsi, A.A. Al-Arfaj, N. Ouerfelli. “Viscosity Arrhenius activation energy and derived partial molar properties in isobutyric acid + water binary mixtures near and far away from critical temperature from 302.15 K to 313.15 K.” Journal of Solution Chemistry 44, (1) (2015) 54-66.. [2] D. Das, Z. Barhoumi, N. Dhouibi, M.A.M.K. Sanhoury, N. Ouerfelli. “The Reduced Redlich-Kister Equations for Correlating volumetric and viscosimetric properties of N,N-dimethylacetamide + N,N-dimethylformamide Binary Mixtures at Temperatures from 298.15 K to 318.15 K.” Physics and Chemistry of Liquids. 50, (6) (2012) 712 – 734..