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Knowledge database: Basics: Melting and boiling point Each liquid has a specific pressure caused by its evaporation, called vapor pressure. The vapor pressure increases as the temperature increases. When the vapor pressure is equal to the external pressure, which in standard conditions equals 101325 Pa or 101.325 kPa, the system reaches its boiling point. Knowing this, one can easily conclude that the boiling point depends on the pressure acting on the system. At a lower external pressure, a lower temperature is required to reach boiling. That's why alpinists, at altitudes of several thousand meters above sea level, notice that water doesn't boil at 100 °C, but already at a lower temperature. This occurs because the atmospheric pressure is lower at higher altitudes. The range of boiling and melting point values in the PTE.
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Basics |