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Chemistry
Vapor pressure -- How does water still boil at 100°C in an open pot?
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[QUOTE="Lnewqban, post: 6828024, member: 673625"] As your intuition correctly noted, the volume of the steam "cavity" tends to infinite for an open container, reason for which no molecules remain close enough to the interphase as to jump back into the liquid (reason for which the liquid eventually disappears from the open container). Nevertheless, the liquid remains pressurized at 1 atmosphere. Any formation of steam still must "fight" against that pressure (which remains constant). This is all about the kinetic energy that the molecules of liquid and vapor have to jump back and forth through the liquid-vapor interphase. We have only two practical ways to measure that molecular energy: temperature and pressure (at constant volume or closed fixed walls container). Vapor pressure is an indirect value that is proportional to the internal kinetic energy of the vaporizing liquid, nothing else. Rather than a cause, it is a consequence of the heat that has been absorbed or yield by the substance, which is what modify the thermodynamic characteristics. [B]For our closed container:[/B] More external thermal energy being transferred into it increases the kinetic energy of each molecule of liquid: measured temperature increases. As a consequence, higher number of molecules, which have higher velocity, jump out of the liquid and into the cavity containing steam or gas: measured pressure increases. We then say that the vaporization phase is initiated and ended at a constant pressure and within a range of fixed temperature values. When balance is reached, exactly the same number of molecules jump back into the liquid (reason for which the level of the liquid remains constant within the closed container). More external thermal energy being transferred into the liquid-vapor mix, or subtracted from it, naturally changes the molecular energy, as well as those previous values of pressure and temperature. Step by step, by modifying the internal energy of the liquid-vapor mix, a curve and a table can be created. Those serve to predict exactly how that mix will behave regarding vaporization and condensation for that substance. Please, see: [URL]https://www.ohio.edu/mechanical/thermo/Intro/Chapt.1_6/Chapter2a.html[/URL] [URL]https://thermopedia.com/content/1150/[/URL][ATTACH type="full" alt="WATER_PROPERTIES_FIG1.gif"]318170[/ATTACH] [/QUOTE]
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Vapor pressure -- How does water still boil at 100°C in an open pot?
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