• Title/Summary/Keyword: 엔탈피

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High Temperature Thermodynamics of Aqueous electrolyte Solutions (전해질 수용액의 고온 열역학)

  • Lee, Man Seung
    • Resources Recycling
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    • v.27 no.2
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    • pp.63-67
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    • 2018
  • Gibbs free energy is a measure of relative stability among substances. Since the nature of the ions in aqueous solution is diverse, their thermodynamic data at extensive experimental conditions is scarce. In this work, the calculation procedure was introduced to obtain the absolute and conventional standard molar enthalpies and entropies of hydration of ions from the standard enthalpies and entropies of formation of hydrated ions. The application of correspondence principle to estimate thermodynamic data at high temperature was explained.

A Proposal of a Correlation of the Enthalpy of Vaporization for Pure Substances and Performance Comparison of Correlations (순수물질에 대한 증발엔탈피 상관식의 제안 및 성능비교)

  • Lee, Kyoung-Youl;Park, Kyoung-Kuhn
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.17 no.12
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    • pp.1185-1191
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    • 2005
  • Published correlation equations of the enthalpy of vaporization are reviewed and a new four-parameter correlation equation is proposed. Performance of the proposed equation is examined using the ASHRAE data for 22 pure substance refrigerants as reference data. The new equation yields an average absolute deviation of $0.05\%$, which is smaller than those of published equations, such as equations of Guermouche-Vergnaund $(0.08\%)$, Aerebrot $(0.13\%)$, Radoz-Lydersen $(0.08\%)$, and Somayajulu $(0.08\%)$. The three adjustable parameters of the modified correlation are optimized and reported for 22 substances. The equation proposed in this work is valid over the entire temperature range where data points exist.

Molecular Orbital Interpretation on the Inhibitory Effect of the Ni(Ⅱ) Complexes with Polyamines and Imidazole Derivatives (Polyamine류와 Imidazole 유도체가 배위된 Ni(Ⅱ) 착물의 저해 효과에 관한 분자궤도함수론적 해석)

  • Kim, Jung-Sung;Song, Young-Dae
    • Journal of the Korean Chemical Society
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    • v.48 no.2
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    • pp.123-128
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    • 2004
  • Quantum chemical quantities, enthalpy of formation(${\Delta}H_f$), HOMO and LUMO energy, and dipole moment(${\mu}_D$) were acquired by AM1, PM3, and ZINDO/1 methods for polyamines and imidazole derivatives. The investigation of the inhibitory activity on some Ni(II) complexes with polyamines and imidazole derivatives is performed by ZINDO/1 calculations. It was found that experimental inhibitory activity(IA) appeared when the value of net charge and enthalpy of formation were over 0.03 and -300 eV, respectively for Ni(II) complexes. These results showed that the Ni(II) complexes have exception on the following very unstable compounds: square pyramidal [Ni(dpt)(tn)])]$^{2+}$(dpt=3,3'-diaminodipropylamine)(tn=1,3-diaminopropane) and distorted tetrahedral [Ni(N-PropIm))$_2$(NCS))$_2$](N-PropIm=N-Propylimidazole).

Differential Scanning Calorimetric Study of Amylose-lipid Complex and Amylose Content in Rice Starch (쌀 전분의 Amylose-lipid Complex 의 DSC 특성과 Amylose 정량)

  • Ko, Jae-Hyung;Park, Kwan-Hwa
    • Korean Journal of Food Science and Technology
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    • v.21 no.4
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    • pp.556-561
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    • 1989
  • Thermal properties of amylose-lysolecithin (AL) complex, amylose content and effect of lysolecithin on the gelatinization of rice starch were investigated by Differential Scanning Calorimetry (DSC). The melting temperature of AL complex was near to $108.5^{\circ}C$ and the melting enthalpy was about 1.0cal/g. The gelatinization temperature of rice starch was not affected by adding lysolecithin. However, the enthalpy of gelatinization was decreased. The amylose contents in rice varieties were calculated from melting enthalpy of AL complex. The amylose contents for Indica and Japonica types of rice were in the range of 16-19%, which were in good agreement with those determined by iodine binding method. Significant differences were not observed in the amylose contents between Indica and Japonica varieties.

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Gelatinization and Retrogradation Properties of Modified Starch by Steeping Sweet Potato (고구마 수침에 의한 변성 전분의 호화와 노화 특성)

  • Lee, Shin-Kyung;Shin, Mal-Shick
    • Korean Journal of Food Science and Technology
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    • v.26 no.5
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    • pp.638-643
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    • 1994
  • Gelatinization and retrogradation properties of modified starches which were prepared by steeping sweet potato at $40^{\circ}C$ for 2, 4, 7 and 10 days were investigated. The peak temperature of gelatinization and enthalpy of untreated starch by DSC were $53.9^{\circ}C\;and\;1.32\;cal/g$, respectively, but those of modified starch were increased by steeping. In gelatinization by alkali, starches with 2, 4 and 7 day steeping showed higher viscosities than untreated starch, whereas the viscosities of starches with 10 day steeping decreased. The clarities in paste decreased during storage in all starches and decreased in starches with steeping. The degrees of retrogradation by ${\alpha}-amylase-iodine$ method were higher in starches with steeping than untreated starch. The enthalpy of retrograded starches by DSC increased by steeping except 4 day steeping starch. The sweet potato extract containing sugar inhibited the retrogradation of starch paste and the degree were higher in residual starches than in untreated starch.

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Thermodynamic Studies on the Structure of Binary Mixed Solvents(Ⅰ). Partial Molal Enthalpies of Alcohol-Cosolvent Mixtures (이성분 혼합용매의 구조에 대한 열역학적 연구(제1보). 알코올-Cosolvent 혼합물의 분몰랄엔탈피)

  • Nah, Sang Moo;Park, Young Dong
    • Journal of the Korean Chemical Society
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    • v.41 no.2
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    • pp.63-68
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    • 1997
  • Calorimetric measurements have been carried out for the binary mixture between protic, ROH (R=Me, Et) and dipolar aprotic solvents, MeCN,$Me_2CO,\;MeNO_2(or EtNO_2)$in order to investigate the molecular interaction and liquid structure of isodielectric solvents. From the measured partial molar enthalpies of the solutions, excess enthalpies for the mixing process were determined. The hydrogen bond strength between two components decreases in the order of$ROH-ROH>ROH-Me_2CO>ROH-MeCN>ROH-MeNO_2(or EtNO_2)$and the hydrogen bond donor acidity decreases in the order of MeOH>EtOH. From this result, we can conclude that the most important interaction for the formation of binary liquid mixture comes from the specific hydrogen bond.

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Effect of molecular and crystalline structure on phase transition behaviors of rice starches (쌀전분의 분자 및 결정구조가 상전이에 미치는 영향)

  • Jeong, Duyun;Lee, Su-Jin;Chung, Hyun-Jung
    • Korean Journal of Food Science and Technology
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    • v.51 no.5
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    • pp.432-437
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    • 2019
  • The objective of this study was to determine the molecular/crystalline structures and phase transition properties of starches isolated from six rice cultivars grown in Korea. Apparent amylose content was highest in starch obtained from the Saemimyeon cultivar (30.8%) and lowest in that obtained from the Sheonhyangheukmi cultivar (20.3%). Starch from the Saemimyeon cultivar had a lower proportion of short chains (DP 6-12) and a the higher proportion of long chains (DP${\geq}37$) than that seen in other rice starches. Saemimyeon had relatively higher pasting temperature ($86.5^{\circ}C$), gelatinization temperature ($72.1^{\circ}C$) and gelatinization enthalpy (14.2 J/g) than these values found for other rice starches. The onset temperature and enthalpy for ice crystallization of rice starch ranged from $-27.1{\sim}-20.2^{\circ}C$ and 241.1~264.8 J/g, respectively. The ice melting enthalpy measured in excess water (67% water content) of rice starches was 282.4~310.1 J/g. Among the rice starches examined, starch obtained from Sheonhyangheukmi, with the lowest amylose content, showed the lowest glass transition temperature (${T_g}^{\prime}$).