You are watching: Why is condensation a warming process

When you"ve finished this page, friend should have the ability to describe the processes of evaporation and condensation, as well as how/why these processes influence temperature. In particular, friend should have the ability to explain temperature and dew allude changes that regularly occur v falling precipitation.


Since evaporation and condensation room such crucial phase alters for water, lock deserve more of our attention. I briefly identified them in the previous section, yet now I desire to take a closer look at at just how these procedures actually work, and what their after-effects are for some weather variables that we"ve currently talked about -- temperature and dew point.

For starters, evaporation is the procedure by which liquid water molecules rest the bond with surrounding molecules and escape right into the air together water vapor, and as I mentioned briefly in the last lesson, evaporation is a cooling process, for a couple of reasons. First, water molecules v the greatest kinetic energy (fastest vibrations) space most likely break the bonds with their neighbors and evaporate, which way the average kinetic energy of the staying liquid water is decreased (because the most energetic molecules space no much longer liquid). A lower kinetic power of the staying water means a lower water temperature. Secondly, the breaking of bonds in between liquid water molecules calls for energy, and that energy comes from the neighboring air.

All the water"s phase changes actually one of two people use power from the neighboring air, or release power to the neighboring air, as portrayed by the "energy staircase" diagram for ice, water, and also water vapor below. Although the diagram includes every one of water"s possible phase changes, we"re walk to emphasis on the two of biggest interest to united state for currently -- evaporation and also condensation. If we start with liquid water, a few highly energetic, free-spirited water molecule can ultimately break the bond with surrounding molecules over time and escape come the vapor phase. Energy is required (600 calories per gram, to be exact) come break all the bonds to allow all the water come rather quickly evaporate and enter the gaseous step of water vapor (the highest power step), i beg your pardon cools the neighboring air.


The power levels linked with ice, water, and water vapor have the right to be thought of as a collection of steps. An altering from one phase (solid, fluid or gas) to an additional requires either an enhancement of energy (stepping up) or a release of power (stepping down).

So, if evaporation is a cooling process, what about its reverse -- condensation (the procedure by i beg your pardon water vapor changes to liquid)? when water vapor condenses earlier into water, there"s a step down in power levels, so if you"re reasoning that condensation is a warming process, you"re yes! Indeed, the power used come evaporate water in the an initial place is never shed (a repercussion of the preservation of energy), so as water vapor condenses right into liquid water and bonds form between molecules, power is exit (600 calories every gram -- similar to the amount required for evaporation) to save the energy publications balanced. The release of this energy, called "latent warmth of condensation," warms increase the neighboring air.

So, any time a phase change (such together evaporation) causes water to walk "up the power staircase," power is required to rest bonds in between molecules, i m sorry cools the surrounding air. Any time a phase change (such together condensation) reasons water to go "down the energy staircase," power is released, which warms up the bordering air.

Lesson learned: Evaporation cools the waiting (because it requires energy, which originates from the surrounding air). Condensation warms the air (because the releases energy to the surrounding air).

The warming that occurs with condensation is not conveniently noticeable to humans, however I bet you"ve i found it the results of evaporational cooling. Once you acquire out the a swimming pool on a hot day, water drops on her skin begin to evaporate, i beg your pardon cools her skin. You"ve additionally noticed evaporational cooling in activity if you"ve ever before felt a rush of cool air before a shower head or thunderstorm arrives. Indeed, temperatures frequently decrease simply before, and also after rain arrives. That"s due to the fact that the the smallest raindrops evaporate along their descent to the ground, i beg your pardon extracts power from the neighboring air.

To see a real-life example, examine out the graph below, i m sorry plots surface ar temperatures and dew points in ~ Louisville, Kentucky ~ above June 11, 2014. I"ve emphasize a sharp drop in temperature (black line) that emerged in the middle of the afternoon, between 1500 and 1600 local time (between 3 P.M. And also 4 P.M.). At 3 P.M. (15:00 top top the graph), Louisville report a temperature that 81 degrees Fahrenheit, however an hour later, the temperature was just 73 levels Fahrenheit.


Surface temperature sharply declined at Louisville, Kentucky, between 3 P.M. And also 4 P.M. Neighborhood time ~ above June 11, 2014 (circled) many thanks to evaporational cooling associated with the start of precipitation. Dew points likewise increased because of network evaporation during this time.

Why did the temperature fall during this hour? Evaporational cooling! It started to rain in between 3 P.M. And 4 P.M., and during the hour, 0.13 inches of rain fell in Louisville, but as precipitation began, evaporation of rain drops cooled the air and temperatures decreased. Likewise note the dew point out increased during the time emphasize in the graph above. Why is that? Well, if liquid raindrops were evaporating right into water vapor, that means more water vapor was present in the air, and also as you may recall, higher concentrations of water vapor go follow me with higher dew points.

You probably don"t establish it, yet evaporation and condensation are occurring about you simultaneously all the time! You simply can"t see the results because they"re keep going on the molecule level. Noticeable phase transforms occur once there"s "net" condensation, definition that the condensation price exceeds the evaporation price (liquid water droplets form), or if there"s "net" evaporation (assuming you have actually some liquid water to start with), which way that the evaporation rate exceeds the condensation rate. The evaporation that rain drops on their descent come the ground is a an excellent example of net evaporation. Small raindrops end up shrinking or disappearing altogether as the rate of evaporation above the rate of condensation.

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Lesson learned: Net evaporation of falling raindrops has tendency to cause decreases in temperature (from evaporational cooling) and also increases in dew point (because of boosts in water vapor from network evaporation).

I should point out that the potential because that evaporational cooling is best when a big difference in between temperature and also dew point exists because huge differences between temperature and also dew point permit for the biggest net evaporation. As temperatures and also dew points obtain closer, net evaporation is reduced, which yields much less evaporational cooling. To really know why this is the case, we require to check out what controls the prices of evaporation and condensation. We"ll carry out that in the following section, as well as see why to compare evaporation rates and also condensation rates is so important to weather forecasters. Check out on!