| json_metadata | "{"app":"Musing","appTags":["science","physics","question"],"appCategory":"science","appTitle":"Why does water boil in a vacuum?","appBody":"<p>As long as the temperature of an object is above absolute zero the molecules it consists of are in motion. Heat energy is random motion of the particles that matter consists of. Temperature is proportional to the kinetic energy of the average particle in matter. The kinetic energy of the particles in an object are unevenly distributed. Some particles have a lot of energy, others have very little and most are close to the average. </p>\n<p>Suppose you have an open vessel filled with water at 1 bar and at 20 C. The quantity of the liquid does not visibly change but some of the water molecules at the surface will always have enough kinetic energy to escape the liquid and become airborne. That process is called evaporation. The process is slowed down by air molecules that exert pressure against the liquid surface (1,013 bar at sea level) by flying against the water surface and colliding into the water molecules trying to escape from the water surface. In a vacuum, there is no gas and thus no gas pressure. When you lower the air pressure, the escaping molecules are hindered less and less by air molecules flying toward them and colliding into them. In a vacuum, there is no resistance from air above the water surface at all. The evaporation quickens and pretty soon there is no liquid water left.</p>\n<p>In space, where there is no gravity, either, the evaporation would be even faster because there would be no gravity pulling the water molecules against the bottom of the can at all.</p>","appDepth":2,"appParentPermlink":"f3upgwbbx","appParentAuthor":"runicar","musingAppId":"aU2p3C3a8N","musingAppVersion":"1.1","musingPostType":"answer"}" |
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