Calorimetric investigation of reaction Ca(NO₃)₂ + Na₃PO₄ in water and microemulsions saturated with CO₂

Abstract

The reactions of Ca(NO 3 ) 2 + Na 3 PO 4 in water and water/sodium bis(2-ethylhexyl) sulfosuccinate (AOT)/hydrocarbon microemulsions saturated CO 2 with various molar ratios of water to surfactant R, oil phases, and surfactant concentrations were investigated by isothermal titration calorimetry. The product of the reaction was confirmed to be sodium-and-carbonatesubstituted hydroxyapatite (NaCO 3 HAP) by Fourier transform infrared spectra (FTIR), energy dispersive spectrometry (EDS), and X-ray diffraction (XRD). From calorimetric measurements, the molar enthalpies of solution of water in the AOT/n-dodecane system, and the molar enthalpies, the rate constants, and the activation energies of the reactions were determined. It was found that the enthalpy of solution of water in AOT/n-dodecane micells and the molar enthalpy of the reaction in the microemulsions increased with the decreases of R until R = 7; below that they kept almost constant. It may be attributed to the increase of the ratio of the bound water to the free water with the decrease of R until there was no free water when R < 7. However, the reaction rate constant k 1 was affected by the ionic strength of the medium and log k 1 showed a linear dependence on 1/R in the whole range of R we investigated. It was also observed that the rate constant and the enthalpy of the reaction remained almost unchanged when the surfactant concentration and the nature of oil phase varied. C

Kinetics of the Reaction of Crystal Violet with Hydroxide Ion in the Critical Solution of 2-Butoxyethanol + Water

“…For a first-order reaction, the reduced extent ψ of the reaction is expressed by ln ( 1 − ψ ) = prefix− k obs t where ψ = ξ/ξ e . ξ and ξ e are proportional to the heat Q produced in the reaction before time t , and the total heat Q ∞ produced in the whole reaction, respectively, and thus ψ = ξ ξ normale = Q Q ∞ A plot of ln(1 – ψ) versus t gave a straight line with a slope being k obs .…”

Kinetics of the Oxidation of Iodide Ion by Persulfate Ion in the Critical Water/Bis(2-ethylhexyl) Sodium Sulfosuccinate/n-Decane Microemulsions

“…Defining a dimensionless reduced extent (Ψ) of the reaction as a ratio of the reaction extent ξ at time t to the reaction extent ξ e at the equilibrium: normalΨ = ξ ξ normale where ξ is proportional to the total heat ( Q ) produced in the reaction before time t for a chemical reaction, thus normalΨ = ξ ξ e = Q Q italice where Q is the heat produced in the reaction before time t and Q e is the total heat produced in the whole reaction.…”

“…where Q is the heat produced in the reaction before time t and Q e is the total heat produced in the whole reaction. For a first-order or a pseudo-first-order reaction, the reduced extent (Ψ) of the reaction could be expressed by 1) obs (22) Therefore, a plot of ln(1 − Ψ) against t should yield a straight line, and the slope is −k obs . Such a plot for the reaction in the microemulsion medium with ω = 35.0 and at T = 313.321 is shown in Figure 2 as an example.…”

“…18−21 Properties of the microreactors can be easily adjusted by varying the size of the droplets. The size of droplets is determined by the molar ratio (ω) of water to surfactant, 22 and the concentration of the droplets in a microemulsion is usually expressed by the volume fraction (Φ), which was assumed to be Φ = Φ w + Φ s with Φ w and Φ s being the volume fractions of water and surfactant, respectively. 23 In this work, we extend the studies of the influence of the critical anomaly on the reaction rate and the equilibrium constant by examining microemulsion media using the microcalorimetry.…”

“…The water in oil (w/o) microemulsion droplets can function as microreactors, which have the capability of enhancing or retarding reaction rates. − Properties of the microreactors can be easily adjusted by varying the size of the droplets. The size of droplets is determined by the molar ratio (ω) of water to surfactant, and the concentration of the droplets in a microemulsion is usually expressed by the volume fraction (Φ), which was assumed to be Φ = Φ w + Φ s with Φ w and Φ s being the volume fractions of water and surfactant, respectively …”