why does water evaporate at room temp

Sometimes a can be sitting in one place (maybe a puddle) and its molecules will become a. That's the process called
evaporation. It can happen when liquids are cold or when they are warm. It happens more often with warmer liquids. You probably remember that when matter has a higher temperature, the molecules have a higher energy. When the energy in specific molecules reaches a certain level, they can have a phase change. Evaporation is all about the energy in individual molecules, not about the average energy of a system. The average energy can be low and the evaporation still continues. You might be wondering how that can happen when the temperature is low. It turns out that all liquids can evaporate at room temperature and normal air pressure. Evaporation happens when or molecules escape from the liquid and turn into a vapor. Not all of the molecules in a liquid have the same energy. When you have a puddle of water (H O) on a windy day, the wind can cause an increased rate of evaporation even when it is cold out.


The energy you can measure with a thermometer is really the average energy of all the molecules in the system. There are always a few molecules with a lot of energy and some with barely any energy at all. There is a variety, because the molecules in a liquid can move around. The molecules can bump into each other, and when they hit. Blam! A little bit of energy moves from one molecule to another. Since that energy is transferred, one molecule will have a little bit more and the other will have a little bit less. With trillions of molecules bouncing around, sometimes individual molecules gain enough energy to break free. They build up enough power to become a gas once they reach a specific energy level. In a word, when the molecule leaves, it has evaporated. The rate of evaporation can also increase with a decrease in the gas pressure around a liquid. Molecules like to move from areas of higher pressure to lower pressure. The molecules are basically sucked into the surrounding area to even out the pressure.


Once the vapor pressure of the system reaches a specific level, the rate of evaporation will slow down. Question: Why does water evaporate at room temperature? Answer: Temperature, as a measurement, tells you the average of how quickly molecules of a given substance are moving around. The phase that a substance will be in at a given temperature is best shown with a phase diagram (see below). [ ] This phase diagram for water shows what state of matter water will be stable in at a given temperature and pressure. You can see the freezing point at 1 atmosphere at 0 C, and the boiling point at 100 C at the same pressure. Interestingly, this is why water will boil at a lower temperature at higher elevations. S ince the atmospheric pressure is lower, it takes less energy for a molecule to break from the liquid phase to the vapor phase. The triple point is a point where water is equally as likely to be in one state of mater as in the others.


It s important to recognize, however, that the phase diagram represents an equilibrium. The fact that water is stable in its liquid state at room temperature and pressure doesn t mean that all of its molecules are stuck in the liquid state. In fact, water is constantly evaporating and condensing. How is this possible? If you remember our definition of temperature from earlier, you ll remember that we mentioned that temperature is an average of kinetic energy. At any temperature above its triple point where water remains liquid, some of the water molecules will be moving comparatively fast (and others comparatively slow). Some molecules will be fast enough to resist the forces of cohesion that loosely bind water molecules together in liquid form. If these molecules happen to be at the surface of the liquid, they are free to escape the cohesive force into the atmosphere and form water vapor, even at room temperature. Answered by Olivia D. , Expert Leader. Edited by Ashlee R.

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