On the heat of reaction between nitrogen dioxide and water
Thread Content
Dear everyone: For work purposes, I need to know the heat of reaction between nitrogen dioxide and water. The reaction equation is as follows: 3NO2 + H2O = 2HNO3 + NO + Q. However, I have found that the value of Q varies significantly depending on the source; for example, in textbooks such as the second volume of High School Chemistry Volume A and \"Inorganic Chemical Engineering Technology\" edited by Chen Wuping, the value of Q is always above 136 kJ/mol； However, when standard enthalpy of formation data are used (from Perry’s Handbook of Chemical Engineering, Standard Tables and Formulas by James G. Spett, 2005, or the tables included at the end of university textbooks on inorganic chemistry), the value comes out to around 71.3 kJ/mol. There is a significant difference between these two values. I was wondering if anyone in the nitric acid industry could tell me which value is more accurate? Thank you so much!
Is it different from the case with catalysts or oxidizers? I don’t understand; let an expert answer
The standard reaction enthalpy at 298.15 K is calculated using standard formation enthalpy data, and can be used when preparing documents on the chemical principles of industrial processes. But it may differ significantly from the heat of reaction data under the actual temperature and pressure conditions required by you. The most important thing to note is that the phase states of the components H2O and HNO3 must be correct; for example, the standard reaction enthalpy value of -71.3 kJ/mol listed by the original poster corresponds to a situation in which H2O and HNO3 are in the liquid phase while the other components are in the gas phase ； If all are gas-phase components, the estimated value of the standard reaction heat is approximately -36.7 kJ/mol. Therefore, it is meaningful to specify the corresponding phase states of the components H2O and HNO3 when listing standard reaction heat data; otherwise, ambiguity will arise. It is estimated that the data mentioned by the original poster, stating that \"Q is above 136 kJ/mol\", refers to the heat of reaction under the actual temperature and pressure conditions, with the components H2O and HNO3 in liquid phase. It is recommended that the original poster use process simulation software such as ASPEN or PRO/II for the calculations, and compare the results with those obtained from reaction heat data; it’s quite simple.
Thank you for your participation. The reaction temperature in this nitrous oxide absorption process is not high, so there is no significant difference from the standard reaction enthalpy; the calculated reaction enthalpies assume that H2O and HNO3 are in liquid state. In my opinion, this difference is not caused by these factors； Additionally, the standard enthalpy of formation in ASPEN yields another set of data that differs significantly; I am not looking for the calculated values, but rather for data that has been verified through practical experience.
The heat involved in the actual nitric acid absorption process includes not only the reaction heat but also the heat of dissolution or dilution; it represents the overall thermal effect of the process. For your reference.
The dilution heat data are relatively certain, with no significant doubts regarding them