Enthalpy‐Concentration diagrams of binary aqueous mixtures of hydrazine, sodium carbonate, and glycerine

Abstract

Generally an enthalpy-concentration diagram for a system is prepared for fixed pressure, and to be complete it should include data on the solid, liquid, and vapor phases. Such charts are useful for calculations involving heat balances with accompanying concentration changes. This article outlines the steps in the preparation of a diagram and includes the diagrams for aqueous solutions of hydrazine, sodium carbonate, and glycerine.Calculation of heat effects accompanying concentration changes in binary solutions can be quickly and easily performed by use of an enthalpy -concentration diagram.Such charts have been called Merkel diagrams after Merkel ( I ) , who was the first t o give a thermodynamic analysis of the chart and who emphasized the use of it in heat-balance calculations. Zeisberg (.2) was perhaps the first to compute enthalpy charts of binary mixtures. Ponchon(3) and Savarit ( 4 ) were the first to use the chart for calculating the number of theoretical plates in a rectifying column.Others have contributed to the use of the chart such as Hirsch (5), who applied it to single-and multiple-effect evaporators, and McCabe (61, who presented the sodium hydroxide-water diagram and reviewed its use in heat-balance calculations. Probably the most complete development of its use was due t u J50Jnjakom(7). He recently applied the diagram to heat-exchange processes in sugar solutions(8) and to chemical processes such as ammonia synthesis ( 9 ) . In summary it might be said that the chart may be used t o solve any binary-mixture problem involving the first law of thermodynamics. The second law of thermodynamics is involved only in the phase-equilibrium portions of the diagram.The principles involved in constructing an enthalpy-concentration diagram, given by Dodge(10) , will be illustrated here by the construction of a diagram for the hydrazine-water system a t 1 atm. The construction requires a complete set of thermochemical data f o r the pure substances and their mixtures over the temperature range desired for the diagram. Lack of such data is the chief reason that there are so few of these diagrams available to industry today. The data required are as follows:1. Complete enthalpy-temperature data for the pure substances. Heat of solution or dilutiondata f o r the binary mixtures. 3. Heat-capacity data for the binary mixtures. 4. Phase-equilibria data for the system if t h e solid or vapor phases are to be included in t h e diagram. As temperatures are frequently measured on the centigrade scale and heat quantities are given in calories in the scientific literature, the most convenient way t o report heat quantities or enthalpies is in d o r i e s per gram of system GT, f o r engineering use, the equivalent, which is centigrade heat units per pound (C.h.u.). The enthalpy results in these units may be converted to British thermal units per pound by multiplying by 1.8. Hnthalpy of Pure SubstancesThe enthalpy data for water are available in tabular form from the work of Keenan and Keyes (11) ; the enthalpy data for...

Enthalpy-Concentration Charts. Literature Survey and the Two New Systems Isopropyl Alcohol-Water and Acetic Acid-Water.

“…hydroxide-water (2, 12,16,22,56,57,62) Chemical equilibria (ammonia synthesis) presented as well.T h i s c o n t e n t i s o n l y l i c e n s e d f o r c o n s u m p t i o n b y A u t h o r i z e d U s e r s a f f i l i a t e i n d i v i d u a l n o t d i r e c t l y a s s o c i a t e d w i t h s c i t e i s p r o h i b i t e d .…”