Activation Entropy Change Research Articles

A Novel Comparative Study: Synthesis, Characterization, and Thermal Degradation Kinetics of a Copolymer and Its Composites with Activated Charcoal

A novel composite was prepared by using a copolymer involving 2-amino 6-nitrobenzothiazole– formaldehyde copolymer and activated charcoal. Physicochemical analysis, elemental and spectrum analysis were used to characterize the produced copolymer and its composite. SEM and thermogravimetric analysis (TGA) was used to study the surface morphology and thermal stability of the copolymer and its composites, respectively. The composite produced better results, which could be attributed to the particle size, porous nature, and increased surface area. The thermal stability of the copolymer and its composite had been improved. The thermodynamic kinetic parameters activation energy, free energy, apparent entropy, frequency factor, and entropy change were also estimated from TG data using the Sharp-Wentworth and Freeman-Carroll methods, and the findings were found to be similar. First-order kinetics were used to decompose the copolymer and its composite. The copolymer and its composite decomposed using first-order kinetics.

Oil produced from Ghana cocoa bean for potential industrial applications

Cocoa bean (Theobroma cacao L.) oil is a promising intermediate cocoa product with few research demonstrating its potential for the direct production of industrial cocoa products. This study highlights the extraction and characterisations of oil obtained from the Ghana cocoa bean crop to evaluate its suitability for industrial applications. A solvent extraction method was employed to extract the oil at variable extraction temperatures and times. Kinetic and thermodynamic models were adopted to study the oil’s extraction at varying temperatures and times. The maximum yield of the oil (21.62%) was reached at the highest temperature, 333 K (at 130 min), following first-order kinetics. The mass transfer (km) and regression coefficient (r2) were 0.0389 ± 0.0045 min−1 and 0.9993 ± 0.0005, respectively. The activation energy (Ea), entropy change (ΔS), equilibrium constant (K), and enthalpy change (ΔH) were 15.57 kJ mol−1, 276.13 J/(mol K)−1, 5.64, and 78.11 kJ mol−1, respectively. The activation enthalpy (ΔH*), entropy (ΔS*), and Gibb’s free energy (ΔG*) were 12.87 ± 0.05 kJ mol−1, − 258.88 ± 0.17 J/(mol K)−1 and 97.13 ± 1.67 kJ mol−1, respectively, favouring a forward, irreversible, endothermic, and spontaneous extraction. The major fatty acids identified in the oil were stearic acid (37%), oleic acid (34%), and palmitic acid (26%). The iodine value, peroxide value, saponification value, unsaponification value, and free fatty acids of the oil were below the recommended standards acceptable for industrial applications. Differential scanning calorimetry–thermal gravimetric studies showed that the oil was thermally stable at high temperatures until thermal decomposition occurred around 260 °C. The oil’s oxidation was monitored with computational modelling and Fourier infrared red spectroscopy, which found the oil highly stable despite the thermal extraction.

Determination of ignition temperature and kinetics and thermodynamics analysis of high-volatile coal based on differential derivative thermogravimetry

In order to accurately determine the ignition temperature (Ti) of coal, Coal spontaneous combustion (CSC) process was tested by a simultaneous thermal analyzer. Next, the abrupt change point of the differential derivative thermogravimetric curve (DDTG) of coal after the high adsorption temperature was taken as the Ti of CSC. Besides, variations of kinetics and thermodynamics during the CSC before and after the Ti were calculated. It was found that the mass loss, heat releases and gaseous products of coal changed slowly before the Ti and surged sharply after the Ti. The coal at ignition temperature was in thermodynamic equilibrium with low activity. However, when the temperature was greater than Ti, the aromatic hydrocarbons in coal begin to decompose, resulting in the increased of active sites and the release of volatiles, and the coal enters an irreversible combustion stage. At this time, upward trends were obtained for the apparent activation energy, pre-exponential factor, enthalpy change, and entropy change, while a gradual decrease was observed for the Gibbs free energy change. Moreover, reaction intensity between oxygen and coal would be increased due to increased of active sites in the coal and enhanced of volatiles release under a slower heating rate.

Highly porous cryogels loaded with bimetallic nanoparticles as an efficient antimicrobial agent and catalyst for rapid reduction of water-soluble organic contaminants

The development of robust materials possessing simultaneously antibacterial and catalytic activities for the reduction and removal of organic pollutants from wastewater with enhanced efficacy has received unwavering interest. Herein, highly porous and thermo-responsive cryogels of poly(N-isopropylacrylamide-co-acryamido-2-methylpropane sulfonic acid) have been fabricated via redox-initiated cryo-polymerization. Silver/gold bimetallic nanoparticles were introduced into a bare cryogel through thermal reduction of metal salts. The fabricated bare cryogels and bimetallic integrated cryogel were confirmed with different techniques including fourier transform infrared spectroscopy. The crystallinity of bare cryogels and bimetallic nanoparticles inside cryogel was examined by using powder X-ray diffraction. Thermo-gravimetric analysis confirmed that bimetallic nanoparticle loaded cryogels were thermally more stable than bare cryogels. The macro-porosity of cryogels before and after loading bimetallic nanoparticles were studied by using scanning electron microscopy. Energy dispersive X-ray and X-ray photoelectron spectroscopy were implemented, confirming the presence of metal elements in the synthesized bimetallic hybrid cryogel. Furthermore, the uniform distribution of silver and gold nanoparticles in cryogel was examined with transmission electron microscopy. The fabricated bimetallic nanoparticle loaded cryogel exhibited high antibacterial activities against E. coli and S. aureus as well as the good catalytic capacity for the rapid reduction of p-nitrophenol and rhodamine B. Catalytic activity was also examined at various temperatures, different pH values and catalyst amounts. The activation energy (Ea = 34.41 kJ mol-1), enthalpy change (ΔH = - 31.92 kJ mol-1) and entropy change (ΔS = −145.19 J mol-1 k-1) of catalytic reduction activation were determined using Arrhenius and Eyring equations. The catalytic performance of bimetallic nanoparticle loaded cryogel was also examined in pure water and tap water. The fabricated bimetallic catalyst was highly stable up to five consecutive cycles without any change in their catalytic performance.

Investigation of the destruction of copolymers of poly(ethylene glycol)fumarate with methacrylic acid using differential equations

In the article the thermal characteristics of a copolymer of poly(ethylene glycol)fumarate with methacrylic acid were studied in a dynamic mode in a nitrogen atmosphere for the first time. A kinetic analysis of the thermal destruction process was carried out using three different data processing methods (Freeman-Carroll, Sharp-Wentworth, Achar). Thermodynamic characteristics were also calculated, namely the change in the Gibbs energy (∆G), enthalpy (∆H) and entropy of activation (∆S). The curves of thermogravimetric and differential thermogravimetric analysis of the copolymer were studied in a nitrogen atmosphere at a heating rate of 10 °C/min. The main stage of the copolymer decomposition was found to occur in a narrow temperature range, which is confirmed by a peak in the differential curve. Changes in the reaction rate of the copolymer were shown due to the decrease in the sample mass. It was shown that the results of kinetic analysis depend on the molecular structure of the compounds under study. The activation energies found by the Freeman-Carroll method have lower values, while the Achar and Sharp-Wentworth methods give the same results.

Determining Preexponential Factor in Model-Free Kinetic Methods: How and Why?

The kinetics of thermally stimulated processes in the condensed phase is commonly analyzed by model-free techniques such as isoconversional methods. Oftentimes, this type of analysis is unjustifiably limited to probing the activation energy alone, whereas the preexponential factor remains unexplored. This article calls attention to the importance of determining the preexponential factor as an integral part of model-free kinetic analysis. The use of the compensation effect provides an efficient way of evaluating the preexponential factor for both single- and multi-step kinetics. Many effects observed experimentally as the reaction temperature shifts usually involve changes in both activation energy and preexponential factor and, thus, are better understood by combining both parameters into the rate constant. A technique for establishing the temperature dependence of the rate constant by utilizing the isoconversional values of the activation energy and preexponential factor is explained. It is stressed that that the experimental effects that involve changes in the preexponential factor can be traced to the activation entropy changes that may help in obtaining deeper insights into the process kinetics. The arguments are illustrated by experimental examples.

Thermodynamic Parameters and Adsorption Mechanism of Corrosion Inhibition in Mild Steel Using Jatropha Leaf Extract in Hydrochloric Acid

Corrosion inhibition performance, thermodynamic parameters and adsorption mechanism of jatropha leaf extract in 2 M HCl solution have been investigated. Inhibition efficiency and corrosion rate were evaluated using gravimetric method, based on ASTM G-31 standards. Activation energy, entropy and enthalpy changes were determined using relevant thermodynamic equations. The mechanism of adsorption was studied using six different adsorption isotherm models. Results obtained show that corrosion rate increased with increase in temperature and decreased with increase in concentration of jatropha leaf extract beyond a maximum dosage. The activation energy of the inhibited process was higher than that of the uninhibited process. The enthalpy and entropy changes obtained were positive and negative, respectively. While the constant of adsorption was positive, Gibb’s free energy change of adsorption was negative with values less than 20KJ/mol. Data obtained fit into Langmuir, Frumkim, El-Awady, Freundlich, Flory Huggins and Tempkin isotherm adsorption models. It was observed that Tempkin model had the best fit and as such was used to evaluate the adsorption constant and Gibb’s free energy change of adsorption. The study found that the adsorption of jatropha leaf extract, on the surface of mild steel, is feasible, spontaneous and follows physical adsorption mechanism.

Thermal investigation of nanospheres and nanowhiskers of CuInS2

The nanospheres and nanowhiskers of ternary CuInS2 are synthesized by sonochemical and hydrothermal techniques, respectively. The energy dispersive X-rays showed the samples to be stoichiometric. The tetragonal unit cell structure of synthesized samples is characterized by X-ray diffraction. The corresponding morphology of the synthesized samples is studied by electron microscopy in scanning and transmission modes. The thermal investigation of the synthesized nanospheres and nanowhiskers is carried out by recording thermogravimetric (TG) and differential thermal analysis (DTA) curves. These simultaneous thermocurves are recorded in temperature range of ambient to 1253 K in an inert nitrogen atmosphere for three heating rates of 10, 15 and 20 K·min−1. The thermal study showed nanospheres to decompose by five steps and nanowhiskers to decompose in a single step. The kinetic parameters like activation energy, phonon frequency factor, activation enthalpy, activation entropy and Gibbs free energy change are determined for both samples. The kinetic parameters are evaluated from the thermocurves data using model-free isoconversion methods like Kissinger–Akahira–Sunose (KAS), Flynn–Wall–Ozawa (FWO) and Friedman (FR). All the obtained outcomes are investigated in details.

Oxidative stability of ternary blends of vegetable oils: A chemometric approach

Unsaturated fatty acids in vegetable oil are prone to lipid oxidation that leads to rancidity, subsequently, the oil's nutritional value is compromised. Edible oils can be tailored to obtain an antioxidant-rich oil blend with better oxidative stability under accelerated storage conditions. In this research, the oxidative stability of the six oil blends containing rice bran oil (RBO: 50–75%), flaxseed oil (FO: 5–10%), peanut oil (PO: 20–40%) at different concentrations is assayed by Arrhenius and Eyring equations (R2 > 0.95, p < 0.05) under Rancimat test conditions (100, 110, 120, 130 °C @ air flowrate 20L/h). The activation energy (Ea), enthalpy change (ΔH), and entropy change (ΔS) of control and oil blends ranged from 74.28 to 93.59 kJ/mol-K, 71.05–90.36 kJ/mol, −41.87 to −100.19 J/mol-K, respectively. Addition of RBO increased tocopherol and oryzanol content in oil blends from 398 to 725 ppm, 0.7 to 1.0 %g, respectively. Hierarchical cluster analysis conferred that RBO-PO-FO: 75-20-5, had better oxidative stability (induction period, IP100: 21.34 h) comparable to RBO with a slower kinetic rate and can be used as a functional oil source. Better understanding of the influence of oil blending on quality traits was delineated by principal component analysis.

Insight into the mechanism of thermostabilization of GH10 xylanase from Bacillus sp. strain TAR-1 by the mutation of S92 to E.

The mechanism of thermostabilization of GH10 xylanase, XynR, from Bacillus sp. strain TAR-1 by the mutation of S92 to E was investigated. Thermodynamic analysis revealed that thermostabilization was driven by the decrease in entropy change of activation for thermal inactivation. Crystallographic analysis suggested that this mutation suppressed the fluctuation of the amino acid residues at position 92-95.

Kinetics and Thermodynamics of Acid Red 1 Adsorption on Used Black Tea Leaves from Aqueous Solution

This study presents the investigation of kinetics and thermodynamics of adsorption of Acid Red 1 (AR1) from aqueous solution on used black tea leaves (UBTL) as a biosorbent. The effects of initial dye concentration, solution pH and temperature on the adsorption kinetics were evaluated through batch adsorption experiments. Different kinetic model equations such as pseudo first order, pseudo second order, Elovic and Intra-particle diffusion were applied to the experimental data to evaluate their validity and determined their respective parameters. The results revealed that the adsorption kinetics is well described by pseudo second order kinetic equation. The equilibrium amounts adsorbed, calculated from the pseudo second order kinetic plots for different initial concentrations, were used to construct the adsorption isotherm which is well expressed by Langmuir equation compared with Freundlich one and the maximum adsorption capacity was 30.03 mg/g. Again, the equilibrium amounts adsorbed, calculated from the pseudo second order kinetic plots for different temperatures, were increased with the increase of adsorption temperature indicating the adsorption is endothermic. The calculated values of apparent activation energy (Ea = 3.35 kJ/mol), enthalpy change (∆H = +30.05 kJ/mol), entropy change (∆S = +0.119 kJ/mol) and free energy change (∆G) revealed that the adsorption of AR1 on UBTL at pH 2.0 was endothermic, spontaneous and physical in nature. The equilibrium amount adsorbed for different initial pH of solution, calculated from pseudo order kinetic plots, was found to be decreased with increase of solution pH from 2.0 to 8.0 suggesting the adsorption mechanism is dominated by electrostatic interaction between positive surface of UBTL at pH 2.0 and negative AR1 dye molecules.

Thermodynamics and adsorption study of the corrosion inhibition of mild steel by Euphorbia heterophylla L. extract in 1.5 ​M HCl

This work investigates the thermodynamics parameters and adsorption mechanism of Euphorbia heterophylla L. extract as a corrosion inhibitor for mild steel in 1.5 ​M HCl. The gravimetric method was used to determine the inhibition efficiency and corrosion rate. Relevant thermodynamic equations were employed to determine the activation energy, enthalpy change and entropy change. The adsorption isotherms were used to evaluate the Gibbs free energy change. Observation from the results of the study showed that the activation energy of an inhibited process was higher when compared with the uninhibited process. Also, the enthalpy change was positive and less than 100 ​KJ/mol threshold. The adsorption study showed that the data fit into the Langmuir, Flory-Huggins, El-Awary’s and Temkin isotherms but Flory-Hugins gave the best fit. The Gibb’s free energy change of adsorption was negative and less than the −20 ​KJ/mol threshold. As concluded from the results, the adsorption of Euphorbia heterophylla L. on mild steel in 1.5 ​M HCl medium is feasible, spontaneous and it occurred by physical adsorption according to Flory-Hugins isotherm model.

Co-combustion behaviors of municipal solid waste and low-rank coal semi-coke in air or oxygen/carbon dioxide atmospheres

Co-combustion characteristics and interactions of municipal solid waste (MSW) and low-rank coal semi-coke (LCSC) in O2/CO2 or air atmosphere are investigated by the thermogravimetric method, including analyses of thermodynamic, kinetic parameters and reaction mechanism function. Results indicated that addition of MSW and higher oxygen concentration improve the co-combustion performance of blends. There are three distinct peaks for co-combustion of blends in air atmosphere, while only two peaks in 30O2/70CO2 atmosphere. It indicates that the presence of CO2 in oxy-fuel atmosphere is conducive to semi-char burnout. Interactions of MSW and LCSC mainly occur between 260 °C and 650 °C, and the synergetic interaction is very obvious around the second peak region of combustion process. The average activation energies Ea show an upward trend with the increase in oxygen concentration, and the minimum value of Ea is obtained when the blend ratio of MSW is 50% which might be an optimal option for co-combustion of blends. Activation energy, enthalpy changes, Gibbs function and entropy changes for 50MSW50LCSC in 30O2/70CO2 atmosphere are 140.86 kJ mol−1, 138.33 kJ mol−1, 161.94 kJ mol−1 and − 41.44 J mol−1 K−1, respectively. In O2/CO2 atmospheres, F6 and F1 functions are more suitable to describe the starting and subsequent process of entail reaction. The results can provide a theoretical and practical guidance for the harmless disposal and resource utilization of MSW and LCSC.

An intensive study on the AC impedance mechanism of (AgPO3)1-x(Ag2SO4)x ionic glass systems under various conditions

PurposeThe purpose of this study is to investigate the effect of the considerable Ag2SO4 content on the electrical and dielectric properties of (AgPO3)1−x(Ag2SO4)x ion glass system as well as to extract thermodynamic parameters.Design/methodology/approachGlass samples of (AgPO3)1-x(Ag2SO4)x with different mole ratios of Ag2SO4 [x = 0.00, 0.10,0.15,0.20 and 0.25] have been synthesized and used. X-ray diffraction and differential thermal analysis were used to investigate structural and thermal properties, and then the electrical characterizations of the bulk glasses were performed in different frequency and temperature range.FindingsFor different ratios of Ag2SO4 on AgPO3, the bulk conductivity is enhanced with increasing the amount of Ag2SO4 until the composition of x = 0.20, after which the conductivity decreases. The general behavior of both ε’ and ε” decreases with increasing frequency and increases with increasing temperature. Complex impedance analysis studied by Z‘−Z’ and Cole–Cole plot at different temperatures revealed that bulk resistance decreases with temperature.Originality/valueThe calculated values of activation free energy, enthalpy and entropy change for different compositions of (AgPO3)1-x(Ag2SO4)x showed an increase in activation energy and enthalpy when Ag2SO4 ratio is increased in (AgPO3)1-x(Ag2SO4)x composition up to 20%, and then there is a decrease in their values at x = 25%, which may be explained based on non-bridging oxygen.

Corrosion inhibition of X80 steel in simulated acid wash solution using glutathione and its blends: Experimental and theoretical studies

In the search for eco-friendly, inexpensive and efficient corrosion inhibitors, glutathione (GLT) and of its formulations with some intensifier compounds were investigated as anticorrosion additives in simulated oilfield scale wash solution. Electrochemical and weight loss techniques were used to monitor corrosion process in-situ, while spectroscopic and microscopic methods were used to characterize corrosion products and surfaces. GLT formed physically adsorbed thin protective film on X80 steel surface and affords efficient corrosion protection, especially as its concentration increased. When added to the aggressive acid wash liquor, corrosion rate, corrosion current and double layer capacitance decreased whereas charge transfer resistance increased due to GLT adsorption on steel surface. GLT worked like a mixed type inhibitor greater inhibitive influence on anodic half reaction. Activation energy, enthalpy, entropy and free energy changes of activation were determined using kinetic and thermodynamic models. With the use of quantum chemical (LUMO-HOMO) calculations, FTIR, SEM/EDS and molecular dynamics simulations, O, N and S sites in GLT molecular structure were confirmed as adsorption sites which facilitate formation of visible protective GLT film on the surface. At temperature as high as 363 K, formulation containing 0.01 M GLT was 89.2% efficient which competed reasonably with a commercial inhibitor.

One-step preparation of reduced graphene oxide/Prussian blue/polypyrrole aerogel and their enhanced photo-Fenton performance

Abstract In this manuscript, hierarchical porous reduced graphene oxide/Prussian blue/polypyrrole (rGO/PB/PPy) aerogel with a surface area of 70 m2/g was prepared and used as a photo-Fenton catalyst. In aerogel, rGO nanosheet acted as skeleton, PPy as cross-linker and PB nanoparticle as active site. The influence of experimental parameters, including H2O2 dosage, rhodamine B (RhB) concentration, catalyst amount, and pH value, on degradation efficiency was investigated. The optimal condition was: 10 mg of catalyst, 10 mg/L of RhB, 100 µL of H2O2, and 6.18 of pH value. Under this condition, 95.2% of RhB was degraded within 30 min and the rate constant was 7.66 × 10−2 min−1. Activation energy, enthalpy change, entropy change, and Gibbs free energy change (298 K) were calculated to be 35 kJ/mol, 35 kJ/mol, 96.5 J/mol K, and 6.4 kJ/mol, respectively. In cyclic experiments, 91.5% of degradation efficiency was remained after the 4th cycle. Besides RhB, other dyes and antibiotics also could be degraded within 75 min. The inhibitory effect of anions was investigated, and H2PO4− had the most significant influence.

One-step preparation of reduced graphene oxide aerogel loaded with mesoporous copper ferrite nanocubes: A highly efficient catalyst in microwave-assisted Fenton reaction.

Heterogeneous Fenton reaction is an attractive method for degradation of organic pollutants due to its high efficiency and non-selectivity and it also causes no secondary pollution. However, low degradation rate and poor recyclability of the catalysts limit its applications for water purification. To overcome this, herein, copper ferrite/reduced graphene oxide (CF/rGO) aerogel was prepared by a one-step hydrothermal method, as a highly efficient catalyst for the microwave-assisted Fenton reaction (MAFR). Under optimal conditions (500 W of microwave power, 600 μL of H2O2, 15 mg of catalyst, and 30 mg/L of RhB), the degradation efficiency of CF/rGO aerogel at 1.0 min (95.7%) was higher than that of reference samples at 3.0 min. Thermodynamical study showed the activation energy, enthalpy change, entropy change, and Gibbs free energy change were 0.73 kJ/mol, -49.5 kJ/mol, -0.135 kJ/mol·K, and -6.8 kJ/mol, respectively, indicating that MAFR was an endothermic and non-spontaneous process.Radical trapping experiments showed that OH, O2-, and h+ played a combined role in RhB degradation. Besides high catalytic activity, CF/rGO aerogel also displayed good reusability, showing removal efficiency of 87.4% after 5 cycles. The high efficiency, good reusability, and simple process make CF/rGO aerogel a promising catalyst for wastewater treatment.

Treatment of soil washing wastewater via adsorption of lead and zinc using graphene oxide.

In the present work, graphene oxide (GO) was synthesized via the modified Hummers method and utilized in treating real soil washing wastewater via adsorptive removal of lead (Pb) and zinc (Zn). Characterization analysis of GO was performed using X-ray diffraction, Brunauer-Emmett-Teller method, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, and zeta potential analysis. The Van't Hoff, Eyring, and Arrhenius equations were applied to determine the activation and thermodynamic parameters namely activation energy (Ea), standard Gibbs energy change (ΔG°), standard enthalpy change (ΔH°), standard entropy change (ΔS°), change in activation Gibbs energy (ΔG#), change in activation enthalpy (ΔH#), and change in activation entropy (ΔS#). Based on the high coefficient of determination values (0.8882 ≥ R2 ≥ 0.9094) and low values of SSE (0.0292 ≤ SSE ≤ 0.0511) and ARE (0.8014 ≤ ARE ≤ 0.8822), equilibrium data agreed well with the Freundlich isotherm. The maximum adsorption capacity for Pb(II) and Zn(II) was determined to be 11.57 and 4.65mg/g, respectively. Kinetic studies revealed that pseudo-second-order equation fitted well with the experimental data, which indicates that chemisorption is the rate-determining step of the adsorption system. Results have shown the possibility of GO as a potential adsorbent material in the treatment of soil washing wastewater.

Adsorptive treatment via simultaneous removal of copper, lead and zinc from soil washing wastewater using spent coffee grounds.

In the present work, the performance of spent coffee grounds (SCG) as an adsorbent in the treatment of real soil washing wastewater (SWW) was evaluated. Scanning electron microscopy, Fourier transform infrared spectroscopy, zeta potential measurement and Brunauer-Emmett-Teller analysis were utilized to determine the physicochemical characteristics of SCG. Maximum removal efficiency of 68.73% for Cu(II), 57.23% for Pb(II) and 84.55% for Zn(II) was attained at 2.5 g SCG, 300 min and 328 K. Error analysis was performed using root mean square error (RMSE) and sum of square error (SSE). Equilibrium data correlated well with the Langmuir isotherm for Pb(II) adsorption and Freundlich model for the removal of Cu(II) and Zn(II). The kinetic study shows that adsorption of the heavy metals using SCG can be satisfactorily described using the pseudo-second order equation (R2 ≥ 0.9901; RMSE ≤ 15.0539; SSE ≤ 145.1461). Activation parameters including activation energy, change in free energy of activation, activation entropy change (ΔS*) and activation enthalpy change (ΔH*) were determined using Arrhenius and Eyring equations. Thermodynamic studies show that adsorption of the heavy metals using SCG is spontaneous, endothermic (ΔH° ≥ 9.80 kJ/mol·K) and results in increased randomness at the solid/solution interface (ΔS° ≥ 2.28 J/mol).

Photometric Study of Oxidation of Ascorbic Acid by Methylene Green in Aqueous Alcoholic System

The photochemical study for oxidation of ascorbic acid with methylene green was studied in aqueous and aqueous methanol, ethanol, and isopropanol at temperature ranges from 303-318 K in acidic medium. The quantum yield of the photochemical oxidation of ascorbic acid with methylene green was determined by irradiation of reaction mixture by monochromatic light of 657 nm and transmitted light was recorded by photocell response as electrical signals on galvanometer. The rate of reaction mixture in terms of quantum yield was determined and found independent of variation in methylene green concentration and had increased with the concentration of ascorbic acid. The effect of dielectric constant was studied by varying the compositions of alcohol and the results obtained revealed that the quantum yield decreased with the decrease of the polarity of system in acidic medium. On the basis of kinetics the reaction follow pseudo first order and mechanism has been proposed. Thermodynamic parameter such as energy of activation (Ea*), change in enthalpy of activation (ΔH*), change in free energy of activation (ΔG*), and change in entropy of activation (ΔS*) were also calculated.