Enthalpy

The aim of the methods described is to calculate the properties of turbulent reactive flow fields. At each point in the flow field, a complete statistical description of the state of the fluid is provided by the velocity-composition joint pdf. This is the joint probability density function (pdf) of the three components of velocity and of the composition variables (species mass fractions and enthalpy). The principal method described is to solve a modelled transport equation for the velocity-composition joint pdf. For a variable-density flow with arbitrarily complex and nonlinear reactions, it is remarkable that in this equation the effects of convection, reaction, body forces and the mean pressure gradient appear exactly and so do not have to be modelled. Even though the joint pdf is a function of many independent variables, its transport equation can be solved by a Monte Carlo method for the inhomogeneous flows of practical interest. A second method that is described briefly is to solve a modelled transport equation for the composition joint pdf.The objective of the paper is to provide a comprehensive and understandable of the theoretical foundations of the pdf approach.

— This experiment aimed determining the enthalpy of neutralization for the strong acid-strong base and weak acid-strong base reactions. Coffee-cup calorimetry was applied to equimolar concentrations of both hydrochloric acid and acetic acid with sodium hydroxide. From the calculated heat capacity of solution, it was found out that the reaction of strong acid-strong base reaction had a mean enthalpy of neutralization of-74844.25 kJ/mol, yielding a percentage error of 28.18%. W eak acid neutralization yielded a value of –73.60 kJ/mol-a percentage error of 12.43%. In the analysis it is assumed that a linear relationship exists in the extrapolation of the final temperature, necessitating stabilities in temperature determinations.

The various state functions that are measurable thermodynamic parameters have been defined and fully explained. The exact differentials of each of the state functions have been derived and their applications clearly examined. The Maxwell Reciprocity Relations have been explained and assessed as to how it provides the conditions for the exactness of each of the state functions. Hence, the application of Maxwell's Relation leads to the provision of new additional thermodynamic formula which is very useful and simple.

The kinetics and mechanism of methylene blue adsorption onto raw pine cone biomass (Pinus radiata) was investigated under various physicochemical parameters. The extent of the methylene blue dye adsorption increased with increases in initial dye concentration, contact time and solution pH but decreases with the amount of adsorbent, salt concentration and temperature of the system. Overall the kinetic studies showed that the methylene blue adsorption process followed pseudo-second-order kinetics among various kinetic models tested. The different kinetic parameters including rate constant, half-adsorption time and diffusion coefficient are determined at different physicochemical conditions. Equilibrium data were best represented by Langmuir isotherm among Langmuir and Freundlich adsorption isotherm. The maximum monolayer adsorption capacity of pine cone biomass was 109.89 mg/g at 30°C. The value of separation factor, R L, from Langmuir equation and Freundlich constant, n, both give an indication of favourable adsorption. Thermodynamic parameters such as standard Gibbs free energy (∆G 0), standard enthalpy (∆H 0), standard entropy (∆S 0) and the activation energy (A) were calculated. A single-stage batch absorber design for the methylene blue adsorption onto pine cone biomass has been presented based on the Langmuir isotherm model equation.

This work considers the seven-coefficient polynomials proposed by the National Aeronautics and Space Administration (NASA) to facilitate obtaining a normalized value for three thermodynamic standard-state specific properties of ideal gases or condenser matters over an interval of temperature. These properties are the heat capacity at constant pressure, the absolute enthalpy (sensible enthalpy plus heat contents due to chemical or physical changes), and the entropy. In the open
literature, one can find several databases for the polynomial coefficients with variation in the number of species included or the range of temperature covered, and this raises a question of whether the choice of a database to use has an important impact on these evaluated thermodynamic properties. Addressing this point, we compare and assess three databases for the NASA 7-coefficient polynomials, over a selected range of temperature from 300 K to 3500 K, and for selected six common gaseous species encountered in combustion or industrial processes, which are molecular oxygen (O2 ), molecular nitrogen (N2
), molecular hydrogen (H2), methane (CH4), carbon dioxide (CO2), and water vapor (H2O). Our comparisons suggest that despite the difference in the values of coefficients, there is no significant difference in their predictions. However, the latest (7th edition) database of Prof. Alexander Burcat hosted at Eötvös Loránd University (ELTE) in Budapest, Hungary
showed superior features when contrasted to other two databases (one accompanying the simulation package OpenFOAM 6, and another provided by the natural-gas reaction mechanism GRI-MECH 3.0).

A method is proposed to estimate the enthalpy of bio-oil in the vapor phase, Hbo, as a function of temperature in the range 298.15–1000 K, of which experimental determination has not been done so far. The two equations proposed in this work allow estimation of the standard enthalpy of formation, Hbo,0, and the difference in the enthalpy between 298.15 K and a given temperature, ΔHbo(T), respectively, only based on the overall C, H, and O contents of crude bio-oil of that N and S contents are lower than 0.5 and 0.1 wt %-daf, respectively. These equations were optimized using thermodynamic data of 290 and 141 organic compounds for Hbo,0, and ΔHbo(T), respectively. Given the yields of bio-oil, char, and gas, elemental compositions of the bio-oil and char, and chemical composition of the gas, proposed equations predict the heat required for biomass pyrolysis, Qpy(Tpy), which is defined as the enthalpy difference between the products at the pyrolysis temperature, Tpy, and the biomass at 298.15 K. The predicted Qpy at Tpy = 773–823 K for five different types of dry biomass was in the range of 1.1–1.6 MJ kg–1.

This study is aimed at identifying and classifying Turkish prospective chemistry teachers’ misunderstandings of enthalpy and spontaneity. In order to fulfill this aim, open-ended diagnostic questions and semi-structured interviews were used after the topic was taught. Diagnostic questions were answered by forty-five students who took physical chemistry courses from two different chemistry education departments in two different universities in Turkey. Seven interviews were carried out just after the administration of the tests. Ten different misunderstandings were identified. Although some of the results of this study confirm the previous research findings, it goes beyond them by identifying new misunderstandings and suggests places where these misunderstandings may originate. The results have implications for tertiary level teaching, suggesting that a substantial review of teaching strategies is needed.

Keywords: Physical Chemistry, Thermodynamics, enthalpy, misunderstandings, misconceptions, undergraduate education, teacher training.

The effect of high-pressure (HP) treatment (100–400 MPa for 15 or 30 min at 20 °C) on the rheological characteristics and colour of fresh and canned mango pulps was evaluated. Differences were observed in the rheological behaviour of fresh and canned mango pulps treated with HP. Shear stress–shear rate data of pulps were well described by the Herschel–Bulkley model. The consistency index (K) of fresh pulp increased with pressure level from 100 to 200 MPa while a steady decrease was noticed for canned pulp. For fresh pulp the flow behaviour index decreased with pressure treatment whereas an increasing trend was observed with canned pulp. Storage and loss moduli of treated fresh pulp with HP increased linearly with angular frequency up to 200 MPa for a treatment time of 30 min while a steady decreasing trend was found for processed pulp. No significant variation in colour was observed during pressure treatment.

I apologize for the format of this paper - it was published as a patent application in order to have it published effectively.

The paper is a trial to formulate a new view to the theory of relativity in order to overcome to issues of 'classical physics' and to close the gap (unify) diverse theories.

Science students find heat, temperature, enthalpy and energy in chemical reactions to be some of the most difficult subjects. It is crucial to define their conceptual understanding level in these subjects so that educators can build upon this knowledge and introduce new thermodynamics concepts. This paper reports conceptual understanding levels of high school students of common thermodynamics subjects such as heat, temperature, enthalpy and energy changes in chemical reactions. The sample of the study was composed of 418 randomly selected students from 11 different high schools. A cross sectional survey model was employed in this study. Data were collected through the Conceptual Understanding Test (CUT), which consists of 16 questions. Cronbach's alpha reliability coefficient for the test was 0.72. Besides, interviews were conducted with 10 students to get qualitative data about their beliefs on the subject. The results of the study indicated that students' level of conceptual understanding in thermodynamics concepts is very low. It was observed to be especially low for the concepts of (1) relationship between energy, enthalpy and bonds in chemical reactions, (2) energy and catalysts in chemical reactions, (3) changes in heat, temperature and enthalpy during change of state, and (4) the relationship between heat, temperature, mass and specific heat. Most of the students in this study do not fully understand common thermodynamics concepts although they have been studying these topics since primary school.

Water hyacinth (WH), an aquatic plant macrophyte, was investigated for its ability to perform as a suitable adsorbent for methylene blue (MB) from aqueous solution. The non-living biomass of WH was subjected to several chemical treatments, namely, washing with hot water, washing with hot dilute HCl, soaking in NaOH, soaking in HNO3, and sulfonation. The system variables studied also include pH and MB concentration. The Langmuir isotherm was found to represent the measured adsorption data well except for WH soaked in NaOH, which was found to be better represented by the Freundlich isotherm. Values of the dimensionless separation factor, K R, indicated that the adsorption systems in this study are all favorable. Values of the first layer of adsorption were calculated by the non-linear multilayer adsorption model, and the specific surface area values were found to be high and comparable to commercially activated carbons.

Adsorption of methylene blue from aqueous solutionsonto unexpanded and expanded perlite samples activatedby H2SO4 and NaCl solutions has beeninvestigated, to assess the possibility of usingperlite for removing cationic dyes from aqueoussolutions. The effects of pH and temperature of dyesolution on the adsorption capacities have beenevaluated. The experimental data were correlatedreasonably well by the Langmuir adsorption isothermand the isotherm parameters (Q m and K) have beencalculated. The removal efficiency (P) anddimensionless separation factor (R) have shown thatperlite can be used for removal of methylene blue fromaqueous solutions, but unexpanded perlite is more effective.

An assessment of the silver–oxygen system has been made, and a consistent set of thermodynamic parameters has been optimized. The calculated thermodynamic properties and phase relations are in good agreement with the experimental data. Ag2O is the only phase that is commonly found within the system. In air, it decomposes to silver and oxygen gas at 420 K. There is a eutectic between silver and Ag2O at a temperature of 804 K, an oxygen partial pressure (PO2 ) of 526 bar (5.26 × 107 Pa), and an oxygen mole fraction in the liquid phase of 0.25. Uncertainties remain on the Ag2O liquidus for PO2 > 108 Pa. An ionic two-sublattice model has been used to describe the liquid phase. This work is part of a study of interactions between compounds from the bismuth– strontium–calcium–copper–oxygen system and silver.

Adsorption of fluoride on waste carbon slurry was investigated. Waste carbon slurry was obtained from fuel oil based generators of a fertilizer industry. The work involves batch experiments to investigate the effects of contact time, pH, temperature and adsorbent dose on the extent of adsorption by carbon slurry. The contact time and pH for maximum fluoride uptake were found 1 h and 7.58, respectively. Maximum adsorption capacity (4.861 mg g−1) of fluoride on carbon slurry was observed at 15.00 mg L−1 initial fluoride concentration using 1.0 g L−1 adsorbent dose. Among four applied models, the experimental isotherm data were found to follow Langmuir equation more closely. Thermodynamically, adsorption was found endothermic with values 7.348 kJ mol−1, −25.410 kJ mol−1 and 0.109 kJ mol−1 K−1 for enthalpy, free energy and entropy, respectively showing the feasibility of adsorption process. From kinetic analysis, the adsorption was found to follow second-order mechanism with rate constant 49.637 g mg−1 min−1. The rate-controlling step of the adsorption was found pore diffusion controlled. In order to investigate the potential of this adsorbent on industrial scale, column and desorption experiments were carried out. The breakthrough capacity of column was calculated 4.155 mg g−1 with at a flow rate of 1.5 mL min−1. The proposed adsorbent has been used to remove fluoride from groundwater and wastewater. Desorption has been achieved under alkaline conditions (pH 11.6) from exhausted carbon slurry. The performance of carbon slurry was compared with many other reported adsorbent for fluoride removal and it was observed that proposed adsorbent is effective in terms of performance and cost especially.

The adsorption of lead onto date palm fibers (palm fibers) and leaf base of palm (petiole) has been examined in aqueous solution by considering the influence of various parameters such as contact time, solution pH, adsorbent dosage, particle sizes, ionic strength, and temperature. The adsorption of Pb(II) increased with an increase of contact time. The optimal range of pH for Pb(II) adsorption is 3.0–4.5. The linear Langmuir and Freundlich models were applied to describe the equilibrium isotherms, and both models fitted well. The monolayer adsorption capacity of Pb(II) on palm fibers and petiole was found as 18.622 and 20.040 mg/g, respectively, at pH 4.5 and 25°C. Dubinin-Radushkevich (D-R) isotherm model was also applied to equilibrium data. The mean free energy of adsorption (2.397 and 4.082 kJ/mol) onto palm fibers and petiole, respectively, may be carried out via physisorption mechanism. Pseudo-first-order rate equation and pseudo-second-order rate equation were applied to study the adsorption kinetics. In comparison to first-order kinetic model, pseudo-second-order model described well the adsorption kinetics of Pb(II) onto palm fibers and petiole from aqueous solution. From the results of the thermodynamic analysis, Gibbs free energy ΔG, enthalpy change ΔH, and entropy ΔS were determined. The positive value of ΔH suggests that interaction of Pb(II) adsorbed by palm fibers is endothermic. In contrast, the negative value of ΔH indicates that interaction of Pb(II) ions by petiole is exothermic. The negative value of ΔG indicates that the adsorption of Pb(II) ions on both palm fibers and petiole is a spontaneous process.