The process of vaporization occurs when molecules have enough heat energy to leave an object and enter the surrounding air. This is an everyday occurrence with water; you see a puddle after it rains, and later the puddle disappears. To varying degrees, evaporation also happens with every other liquid and solid given the right conditions. For solids, the process is called sublimation: the substance turns into a gas without first becoming a liquid.
The metallic element mercury is liquid at room temperature and standard atmospheric pressure. In the open, it slowly gives off a toxic vapor; this is one reason manufacturers have discontinued its use for thermometers, barometers and many other applications. It still has use in fluorescent lighting, however; mercury vapor in a sealed glass tube conducts electricity and produces light with high efficiency.
Liquid nitrogen is an inexpensive cryogenic liquid that has a temperature of -196 Celsius (-320 Fahrenheit), which is very near its boiling point. When exposed to room temperature, the liquid boils vigorously, giving off an invisible nitrogen vapor. If you spill some liquid nitrogen on the floor, it makes a puddle, then vanishes in a few seconds. Heat from the room enters the puddle, raises its temperature, and causes the liquid to evaporate.
Any substance evaporates when the most energetic molecules at the surface produce pressure greater than that of the surrounding atmosphere. Molecules with this much energy literally fly off the surface. When you open a bottle of alcohol, you will quickly smell its pungent odor as it evaporates. The boiling point depends on the type of alcohol and generally falls in a range of about 65 to 117 degrees Celsius (149 to 243 degrees Fahrenheit). However, alcohol does not need to boil to evaporate as long as some of its molecules have enough energy to leave the liquid.
Although the element tungsten has a boiling point of 5,660 degrees Celsius (10,220 degrees Fahrenheit), it too evaporates given the right conditions. An incandescent light bulb’s tungsten filament operates in a near vacuum. When you turn the light switch on, an electric current heats the filament to about 1,700 to 2,700 degrees Celsius (3,100 to 4,900 degrees Fahrenheit), producing white light. The light bulb contains a vacuum, so tungsten atoms have little pressure to overcome to leave the filament. Atoms of tungsten evaporate from the filament, but because it happens in a confined space, they return to the filament when the light is off. Over time, however, some of the evaporated tungsten collects on the inside surface of the light bulb and the filament becomes thinner and weaker. An old light bulb takes on a dark grayish color from the accumulated tungsten on the glass. Eventually the filament breaks from having lost too much material.
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