if weput water in a vacuum chamber so that the rate of boiling is high enough, we se that water boils and freezes at the same temperature... explain what happens??
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This sample was evacuated in preparation for vaporizing the fluid for mass spectrometry, decreasing the pressure and, consequently, the boiling point temperature. It turned out that this pressure/temperature combo was near the substance's triple point, the particular temperature and pressure at which the three states of matter (solid, liquid, and gas) exist in thermodynamic equilibrium. As the liquid boils, high energy molecules leave the liquid as gas, lowering the temperature of the liquid left behind and causing it to freeze. This process of boiling and freezing continues while the substance remains at this pressure and temperature.
Edit: I was mistaken when I referred to this as the triple point, as we would not be seeing phase changes at the triple point. Instead, we're seeing phase changes near the triple point; at this particular pressure, the temperatures required for freezing and vaporization are very close. At the true triple point, the three states are in perfect equilibrium, which can be tricky to achieve, as you can see below:
Edit: I was mistaken when I referred to this as the triple point, as we would not be seeing phase changes at the triple point. Instead, we're seeing phase changes near the triple point; at this particular pressure, the temperatures required for freezing and vaporization are very close. At the true triple point, the three states are in perfect equilibrium, which can be tricky to achieve, as you can see below:
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