Differential enthalpies of absorption of CO2 in aqueous ammonia were predicted based on reaction equilibrium constants using the Gibbs-Helmholtz equation. The reaction equilibrium constants were selected from the literature and integrated into an electrolyte-NRTL model and the model proposed by Edwards, in which the interaction parameters were previously and solely fitted from the NH3-CO2-H2O vapor liquid equilibrium (VLE) data. The heat contributions of the individual reactions were taken into account in the total heat of absorption in both of the models. The heat of absorption was presented as a function of the CO2 loading and temperature. The predicted heats of absorption were compared with experimental data for temperatures ranging from 35 to 80 degrees C obtained in this work and also some other modeling results. The predicted results fit the experimental data well at lower temperatures, and also well at lower loadings when the temperature was higher. but the model was not good at high loadings and high temperature. The paper suggested that the heat of absorption data should also be included when parameters were fit together with VLE data in order to predict the heat of absorption well over a wide range of temperatures and loadings.