State Functions: Interactive Simulation
This simulation was prepared using Mathematica. Download the free Wolfram player, and then download the simulation CDF file (link given below or click on figure to download). A screencast below explains how to use this simulation.
This simulation uses the state function concept for enthalpy to determine how much water freezes during evaporative cooling; its picks a pathway that makes the calculation easier. Water evaporates when the pump decreases the water partial pressure below its saturation pressure. The energy to evaporate water is obtained by cooling the remaining liquid water, and then freezing some liquid when the temperature reaches 0°C. The bar graph on the right shows the amounts of liquid and solid water in the tank and the amount of vapor that evaporated. In the tank, the remaining liquid is blue and the solid is green.
Try to answer these questions before determining the answers with the simulation. We suggest that you write down the reasons for your answers.
- A well-insulated tank with a valve on top contains 10 kg of liquid water at 0°C. A vacuum pump removes 1 kg of water vapor. The heat of vaporization at 0°C is 2,500 kJ/kg and the heat of fusion is 330 kJ/kg. What is the temperature of the remaining 9 kg? What phase or phases are the remaining 9 kg?