Correlating vapor pressures and heats of solution for the ammonium nitrate—water system: An enthalpy–concentration diagram

Abstract

AbstractThe usual tedious method of construction of enthalpy‐concentration charts for solutions of solids requires data seldom available. A new, simple method is therefore presented that utilizes more readily available data, that is vapor pressures of the solutions. These plot as straight lines on a logarithmic‐reference substance plot. Differences from unity of the slopes of these lines represent heats of solution, and when this difference function is integrated between concentration limits the integral heat of solution is obtained. The enthalpy chart is then readily constructed by use of the specific heats of liquid and solid.Ammonium nitrate is the solid used in this example, and water is the liquid because of the industrial importance of aqueous solutions. Vapor pressures were carefully determined experimentally, and the enthalpy chart was developed from the straight lines of the logarithmic plot and available heat data. Constants for the vapor‐pressure curves for ammonium nitrate solutions and equations for enthalpies of solid ammonium nitrate are given for the temperature range 0° to 170°C.