• Bulletin of the Korean Chemical Society
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• v.16 no.5
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• pp.432-436
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• 1995

The solubility of caffeine in compressed carbon dioxide has been measured to determine its fugacity coefficient between 330 and 410 K up to 500 bar. The result allows the calculation of the thermodynamic excess functions such as the molar excess enthalpy, the molar excess free energy, and the molar excess entropy. The pressure variations of the molar excess functions of caffeine in the caffeine-CO2 mixture were discussed and also compared them with those in the caffeine-NH3 mixture.

• Journal of the Korean Vacuum Society
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• v.3 no.2
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• pp.198-202
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• 1994

Zn0.5Mg0.5Te 및 Zn0.5Mg0.5Te:Co 단결정을 온도진동법을 응용한 화학수송법으로 성장시켰고, 광 학적 energy gap의 온도의존성은 Varshni의형식에 잘 적용되었다. 광학적 energy gap의 온도의존성으 로부터 열역학 기본함수인 entropy, enthalpy, heat capacity를 구했다.

• YAKHAK HOEJI
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• v.14 no.1_2
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• pp.36-43
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• 1970

Imidazole및 유사화합물과 천이원소간의 착염형성은 생화학적으로도 중요한 문제다. 본 논문은 Cd, Ni, Mn, Co등과 착염형성을 polarograph법으로 구명하였으며 착염형성 상수는 deford및 Hume의 수학적방법을 적용하여 계산하였다. 착염형성에서의 enthalpy 변화, .DELTA.H$^{.deg.}$ , 및 entropy변화, .DELTA.S$^{.deg.}$ 를 25.deg.C와 35.deg.C의 실험에서 얻은 결과로부터 구하였다.

• Bulletin of the Korean Chemical Society
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• v.8 no.1
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• pp.31-39
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• 1987

By using a complete rate constant($k_e$) which treats a solvent (water) as a reactant, and a conventional rate constant($k_c$), which ignores the solvent in describing the rate, the parameters ${\Delta}V^{\neq}_s,\;{\Delta}H^{\neq}_s\;and\;{\Delta}S^{\neq}_s$ were introduced. These quantities represent the volume change, the enthalpy change, and the entropy change accompanying the electrostriction which occurs when solvent molecules condense on the activated complex. The authors measured the rates of the solvolysis of benzoyl chloride in water-acetone mixtures at $15^{\circ}$ to $30^{\circ}C$ and 1 bar to 2500 bars. Applying the authors' theory to the experimental results, the parameters, ${\Delta}V^{\neq}_s,\;{\Delta}H^{\neq}_s\;and\;{\Delta}S^{\neq}_s$ were evaluated, and it was found that they are all negative, indicating that water dipoles condense on the activated complex. They also proposed the following equations: ${\Delta}H^{\neq}_c\;=\;{\Delta}H^{\neq}_e\;+\;{\Delta}H^{\neq}_s\;and\; {\Delta}S^{\neq}_c\;=\;{\Delta}S^{\neq}_e\;+{\Delta}S^{\neq}_s\;,\;where\;{\Delta}H^{\neq}_c\;and\;{\Delta}H^{\neq}_c\;and\;{\Delta}S^{\neq}_s $are the activation enthalpy change and the activation entropy change for the conventional reaction rate, respectively, and ${\Delta}H^{\neq}_e$ and ${\Delta}S^{\neq}_e$ are the corresponding quantities for the complete reaction rate. The authors proposed that for the $SN_1$ type, all the quantities, ${\Delta}V^{\neq}_s,\;{\Delta}S^{\neq}_s\;,{\Delta}H^{\neq}_s\;and\;{\Delta}S^{\neq}_s$ are comparatively large, and for the $SN_2$ type, these quantities are smaller than for the $SN_1$ type, and occasionally the case ${\Delta}S^{\neq}_e$ < 0 occurs. Using these criteria, the authors concluded that at high temperature, high pressure and for a high water content solvent, the SN_1$ type mechanism predominates whereas in the reversed case the $SN_2$M type predominates.

• Corrosion Science and Technology
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• v.21 no.5
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• pp.381-389
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• 2022

Cyclic Voltammetry and weight loss measurements were used to investigate corrosion prevention of tin in a 0.5M citric acid solution containing Anthocyanins extracted from grapes at various concentrations and temperatures. Results showed that the investigated chemicals, Anthocyanins extracted from grapes, performed well as tin corrosion inhibitors in 0.5M citric acid. Increasing the concentration of Anthocyanins increased their corrosion inhibition efficiencies. When the temperature dropped, their inhibition efficiencies, increased indicating that higher temperature tin dissolution predominated the adsorption of Anthocyanins at the surface of tin metal. When inhibitor concentrations were increased, their inhibition efficiencies were also increased. These results revealed that corrosion of tin metal was inhibited by a mixed type of adsorption on the metal surface. The adsorption isotherm of Langmuir governed the adsorption of Anthocyanins. Thermodynamic parameters such as the enthalpy of adsorption, the entropy of adsorption, and Gibbs free energy and kinetic parameters such as activation energy, enthalpy of activation, and entropy of activation were computed and discussed in this study.

• Bulletin of the Korean Chemical Society
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• v.26 no.8
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• pp.1246-1250
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• 2005

We have evaluated the hydroxyl group-solvent specific interactions by using a Lichrosorb RP18 stationary phase and by measuring the retention data of carefully selected solutes in 50/50, 60/40, 70/30, 80/20, and 90/10(v/v%) methanol/water eluents at 25, 30, 35, 40, 45, and 50 ${^{\circ}C}$. The selected solutes are 3 positional isomers of phenylpropanol, that is, 1-phenyl-1-propanol, 1-phenyl-2-propanol, and 3-phenyl-1-propanol. There exist clear discrepancies in ${\Delta}H^o$ (solute transfer enthalpy from the mobile to the stationary phase) and $T{\Delta}S^o$ (solute transfer entropy) among positional isomers. The difference in ${\Delta}H^o$ and $T{\Delta}S^o$ between secondary alcohols (1-phenyl-1-propanol and 1-phenyl-2-propanol)is negligible compared to the difference between the primary alcohol (1-phenyl-3-propanol) and secondary alcohols. The $T{\Delta}S^o$ values of 3-phenyl-1-propanol are close to those of butylbenzene while the $T{\Delta}S^o$ values of secondary alcohols are close to those of propylbenzene. The difference in ${\Delta}{\Delta}H^o$ (specific solute-mobile phase interaction enthalpy) between the primary alcohol and the secondary alcohol decreases with increase of methanol content in the mobile phase. A unique observation is an extremum for 1-phenyl-3-propanol in the plot of $T{\Delta}{\Delta}S^o$ vs. methanol volume %. The positive sign of $T{\Delta}{\Delta}S^o$ of 3-phenyl-1-propanol implies that the entropy of 3-phenyl-1-propanol is greater than that of the hypothetical alkylbenzene (the same size and shape as phenylpropanol) in the mobile phase.

• Journal of The Korean Association For Science Education
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• v.26 no.7
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• pp.805-812
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• 2006

In this study the description patterns of chemistry textbooks on the boiling point elevation phenomenon and the understanding patterns of high school students, pre-service teachers and chemistry teachers were investigated. High school chemistry II textbooks developed in the 6th and 7th national curricula were analyzed and the conception patterns of subjects on this phenomenon were categorized using a questionnaire developed for this study. The description patterns of science textbooks were classified into three: 'decreasing of surface solvent molecules', 'attraction force between solvent and solute molecules' and 'decreasing of surface solvent molecules and attraction force between solvent and solute molecules'. In the result of the conception analysis, the ratio of 'attraction force between solvent and solute molecules' was high among students, pre-service teachers, and chemistry teachers. There was a propensity that they would like to explain the boiling point elevation in terms of enthalpy rather than entropy, and in order to analyze this propensity, follow-up interviews were carried out.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.3
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• pp.459-466
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• 2006

Numerical values of thermodynamic properties such as temperature, pressure, dryness, volume, enthalpy and entropy are required in numerical analysis on evaluating the thermal performance. But the steam table itself cannot be used without modelling. From this point of view the neural network with function approximation characteristics can be an alternative. the multi-layer neural networks were made for saturated vapor region and superheated vapor region separately. For saturated vapor region the neural network consists of one input layer with 1 node, two hidden layers with 10 and 20 nodes each and one output layer with 7 nodes. For superheated vapor region it consists of one input layer with 2 nodes, two hidden layers with 15 and 25 nodes each and one output layer with 3 nodes. The proposed model gives very successful results with ${\pm}0.005%$ of percentage error for temperature, enthalpy and entropy and ${\pm}0.025%$ for pressure and specific volume. From these successful results, it is confirmed that the neural networks could be powerful method in function approximation of the steam table.

• Analytical Science and Technology
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• v.11 no.2
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• pp.92-95
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• 1998

K-SGICs(synthetic graphite intercalation compounds) were synthesized in a modified two-bulb pyrex tube. The pressure in the two-bulb tube was maintained at approximately $10^{-3}$ torr for the reaction of potassium and graphite. Deintercalation process of the K-SGlCs obtained by the modified method was heat-treated by keeping in liquid paraffin between $25^{\circ}C$ and $1400^{\circ}C$. The thermal stability and the temperature dependence of the K-SGICs were characterized using differential scanning calorimeter(DSC) analyzer. Enthalpy and entropy for K-SGIC formations were calculated by confirming the deintercalation and thermodynamic exothermic reactions depending on the various temperatures. The structure changes and thermal stability of K-SGICs during the deintercalation reaction of potassium ions and the interlayer spaces of the synthetic graphite were identified by X-ray diffraction(XRD).

• Textile Coloration and Finishing
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• v.12 no.1
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• pp.52-60
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• 2000

In the prior studies, we reported that the dye uptakes of C. I. Disperse Violet 1 on polyester fiber in hexane and cyclohexane were higher than those in the other solvents, as the number of carbon atoms of alkanes decreased, the dye uptake increased, and the logarithmic plot of the dye uptakes vs. the solubilities of the dye showed that the dye uptakes are inversely proportional to the solubilities. In this study, for Interpretation of dyeing behavior of C. I. Disperse Violet 1 on polyester in alkanes, the thremodynamic parameters of dyeing, such as standard affnity, heat of dyeing(enthalpy change), entropy change, diffusion coefficient, and activation energy of diffusion, were obtained from isotherms and dyeing rates at different temperature. As the number of carbon atoms of alkanes increased, the standard affinity decreased, but the heat of dyeing(enthalpy change) and the entropy change showed larger negative values. These results mean that as the number of carbon atoms of alkanes increases, the dye uptake decreases, but both the fraction of the dye molecules dyed at relatively highly aligned or compact region of polyester fiber and the regularity of dye aggregates in the fiber become increased. As the number of carbon atoms of alkanes increased, the diffusion coefficient decreased, but the activation energy of diffusion increased. In the alkane of larger number of carbon atoms, because the solubility of the dye is higher, the desorption rate of the dye is faster and the diffusion coefficient is smaller than those in the smaller alkanes. But the energy required to separate the dye molecules from the alkane molecules is much higher because the interaction between the alkane molecule and the dye molecule become strong with the number of carbon atoms.