Final answer:
The equilibrium constant for the phase change of water from liquid to gas at 30 °C is not directly provided. To find this value, one would typically use an appendix with thermodynamic data. Qualitatively, the equilibrium constant at 30 °C would be expected to be lower than at 60 °C, where Kp is 0.196, since the phase change is endothermic.
Step-by-step explanation:
The student is asking about the value of the equilibrium constant expression for the phase change of water from liquid to gas at 30 °C. The equilibrium constant for a reaction quantifies the relative amounts of reactants and products at equilibrium.
In this case, the data that are provided is for 60 °C, where Kp = 0.196, but the question asks for the value at 30 °C, which is not directly provided. To determine the value at 30 °C, one would typically consult an appendix of thermodynamic data (in this case, Appendix E) to find the vapor pressure of water at that temperature or to look for the specific K value at that temperature.
Since we do not have Appendix E, we cannot provide an exact value; however, it is well understood that the equilibrium constant varies with temperature, often increasing for endothermic processes as temperature increases, and decreasing for exothermic processes as temperature decreases.
The phase change from liquid to gas (H₂O(l) ⇒ H₂O(g)) is endothermic. Therefore, we can qualitatively say that the Kp for the phase change at 30 °C would be less than 0.196, assuming that the trend follows the typical behavior of an endothermic process.
One would consult a vapor pressure table or chart specific to the substance in question and use the Clausius-Clapeyron equation or a variation thereof, to estimate Kp at different temperatures.