CHEG231-F22 Homework Solution 2

CHEG 231, Fall, 2021 Homework Assignment #1 – Solutions & Rubrics Problem 2: (a) Search online for the enthalpy change upon fusion for water and then use the Steam Tables to show that this value is consistent with the relationship. ΔĤ subl H2O,tp - ΔĤ vap H2O,tp = ΔĤ fus H2O,tp ΔĤ vap H2O,tp =2501.3J/g, ΔĤ subl H2O,tp =2834.8 2501.3-2834.8= -333.5J/g -334kJ/kg according to Young, Hugh D., University Physics, 7th Ed., Addison Wesley, 1992. (b) Search for the enthalpy changes for vaporization, fusion, and sublimation for your project compound at the triple point and show that ΔĤ subl tp - ΔĤ vap tp - ΔĤ fus tp =0 if all three values are available. If the information needed is not all available, which will be the case for most or all of the project compounds, you may need to use predicted values and/or make some assumptions to approximate the values. If you can find just two of the three enthalpy changes, you can use those to determine the missing one by using the relationship above. It may be useful to see that the triple point temperature is usually very close to the normal melting point. You may find that the enthalpy of vaporization is reported at room temperature and perhaps some other temperatures, but not at the triple point; if so, note that the largest value occurs at the triple point. You may need to extrapolate to obtain an estimate. These results will be useful for your project report! Using ammonia as the reference compound and the same logic as previously, ΔĤ fus tp of ammonia at the triple point is 332.16 Kj/Kg and the ΔĤ vap tp is 1369.8 Kj/Kg from knovel.com. By understanding that sublimation = vaporization -fusion, we can get ΔĤ subl tp of ammonia at the triple points as 1701.96 Kj/kg which is similar to literature reported values of 1718 Kj/Kg.