Evaporation occurs when water molecules move fast enough to escape their liquid state and become vaporous. Three major variables control rate of evaporation: the temperature of the liquid, which directly affects the velocity of the water molecules, the surface area of the liquid, which affects how much interchange can occur with the air, and the atmospheric pressure. ("EVAPORATION, SURFACE AREA, TEMPERATURE, AND SEAWATER ", n.d.)
Water molecules are always moving; at the water's surface, some molecules are bumped by molecules below them and gain enough speed to break free and escape into the air as gas [water vapour]. This escape of surface molecules is called evaporation ... it involves a change of state, from liquid to gas.
Evaporation takes place all the time and at any temperature.The higher the temperature, the higher the rate of evaporation. When the temperature of water is increased (e.g., shining a powerful spotlight at it), the water molecules gain more energy, move faster and escape at a faster rate.(Alan & Hui Meng, n.d.)
Heat affects rate of evaporation.(Kurup P., n.d.)
As the temperature of air is increased, its capacity to hold moisture also increases. Any increase in air temperature raises the temperature of water at the evaporation source which means that more energy is available to the water molecules for escaping from liquid to a gaseous state. Hence evaporation is directly proportional to the temperature of evaporating surface. Warmer the evaporating surface, higher the rate of evaporation
Heat (energy) is necessary for evaporation to occur. Energy is used to break the bonds that hold water molecules together, which is why water easily evaporates at the boiling point (212° F, 100° C) but evaporates much more slowly at the freezing point. Net evaporation occurs when the rate of evaporation exceeds the rate of condensation. A state of saturation exists when these two process rates are equal, at which point the relative humidity of the air is 100 percent. (U.S. Department of the Interior and U.S. Geological Survey, 2014)
Evaporation is caused by heat, the energy of molecules in motion. Molecules are motionless at absolute zero (-459.67 F. [-273.15 C.]). Above that temperature they are in constant motion, and the higher the temperature the faster they move. In moving, the molecules bump into each other. With each collision they transfer energy. If a surface molecule is bumped by two or three others in quick succession, it may gain enough energy to escape into the air, or evaporate. An evaporating molecule takes energy with it. Loss of this energy cools the substance from which it escapes.
The larger the exposed surface area, the higher the rate of evaporation.(Alan & Hui Meng, n.d.)
Increase in surface area exposed assists evaporation; for instance, a wet cloth spread out dries faster than when folded.(Kurup P., n.d.)
Surface Area The rate of evaporation is determined by the area of the exposed surface of water. Larger areas of evaporating surface increase the rate of evaporation.("Evaporation", 2013)
Direct light will lead to more evaporation. The direct photons of light increase the motion of the water molecules it strikes giving them a better chance to evaporate. (Jeff H., n.d.)
Uses of evaporation
Also in our everyday life, the use of evaporation plays a part in 'Refrigeration', which is common for keeping food fresh as in the Household Fridge, in air-conditioning for keeping buildings cool and, in freezers used to provide us with ice for cold drinks and to preserve food for long periods of time.
In industry, the principles of evaporation and refrigeration are used to great extent in the treatment, separation, handling and storage of materials in any of the three states of matter - Solid, Liquid or Gas. Distillation concerns the separation of liquid mixtures by evaporation processes.
|Test||Control||Light (decrease)||Surface Area (decrease)||Temperature of hotplate (decrease)||Wind (increase)||Purity (decrease)|
|Average amount of water evaporated||32.7||27.7||16||3||34.7||39|
|Rate of evaporation per min||3.27||2.77||1.6||0.3||3.47||3.9|
|Difference from control||0.5||1.67||2.97||0.2||0.63|
|Results are the amount of water evaporated.|
|Average amount of water evaporated||Rate of evaporation per min||Difference from control||In ascending order of difference|
|Purity(decrease)||39.0(3SF)||3.9ml||0.63||Temperature of hotplate|
|Temperature of hotplate(decrease)||3||0.3ml||2.97|