Precipitation–dissolution theory was employed to explain this phenomenon. Solution-grown crystals exhibit a stoichiometry that depends on the solvent used and not on the initial stoichiometry of the perylene and TCNQ: only single crystals of P1T1 were grown from toluene, and only P3T1, from benzene. Using a physical vapor transport (PVT) method, mixtures of P1T1 (perylene1–TCNQ1), P2T1 (perylene2–TCNQ1), and P3T1 (perylene3–TCNQ1) crystals can be grown simultaneously. Perylene forms three binary compounds with TCNQ. Entropy and Enthalpy values were also changed in mixed solvent systems. On the other hand Go values were linearly increased against percentage composition of mixed solvents systems. Furthermore, methanol produced minimum decreased due to its high value of dielectric constant while in 2-propanol showed maximum decreased in solubility and KSP values. The solubility of Ca(OH)2 was decreased at higher temperature compared to room temperature. This represents that solubility and KSP values are linearly decreased. It was found that the equivalence point was decreased linearly by the increasing of the percentage composition of the mixed solvents systems. In the present study the dissolution of calcium hydroxide (Ca(OH)2 in water as well as in mixed solvents systems such as (methanol + water), (ethanol + water), (1-propanol + water) and (2-propanol + water) in 0-25 percentage compositions range at 293 ± 1K and 343 ± 1K or (328 ± 1K in case of methanol) was undertaken for the determination of solubility, solubility product constant (Ksp),Gibbs free energy change (ΔGo), entropy change (ΔS°) and enthalpy change (H°) by pH-metric method.
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