Can you please explain why the solid phase is the thermodynamically stable one here? I'm confused by the explanation. I understand the concept: for a given temperature and pressure the phase that exists is the most thermodynamically stable. However, the "given temperature and pressure" for the freeze-dried product in experiment 2 are not provided in the passage. So how do we know that the frozen sample that is placed in the chamber is the thermodynamically stable phase?
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As you state, to know the most thermodynamically stable state, you'd have to be provided a temperature and a pressure to be able to use the phase diagram they handily provide in the passage. We are actually given this information -- the pressure is given in the question stem ("at an initial pressure of 1 atm"), and the temperature is given in the passage in Experiment 2 ("placed in an identical chamber at -20 degrees Celsius"). Using the diagram, we're at 253 K and 1 atm. This is pretty close to the solid/liquid line shown there. So what do we do?
Well, use what you know. If the water is a solid before they even put it in the -20 C container ("The sample is frozen and placed in..."), it's definitely going to be solid at -20 C and 1 atm.
Make sure when you read passages, to highlight the numbers, especially in experimental passages. You can easily find it that way, without copying down all the variables on your scratch paper.
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