Why do puddles evaporate? If the boiling point of water is 100oC. But water evaporates on warm days - explain

Answer 1

Evaporation, gradual change of state from liquid to gas that occurs at a liquid’s surface. Examples of evaporation include rainwater evaporating from warm pavement after a thunderstorm and wet paint drying as solvents in the paint evaporate. Fingernail polish also hardens as acetone (CH3COCH3) evaporates from the liquid polish.

A liquid is made up of atoms or molecules (bound groups of atoms) that are in constant motion, traveling at different speeds. The average speed of these particles depends only on the liquid’s temperature. If the particles have enough energy, fast-moving particles striking other particles near the liquid’s surface may impart enough speed, and therefore enough kinetic energy (energy of motion) to cause the surface particle to leave the liquid and become gas atoms or molecules. The particle’s kinetic energy is directly related to its speed.

As particles with the most kinetic energy evaporate, the average kinetic energy of the remaining liquid decreases. In a similar way, if a basketball team loses its tallest players, the average height of the team is diminished. Because a liquid’s temperature is directly related to the average kinetic energy of its molecules, the liquid cools as it evaporates

Answer 2

Water can evaporate at ambient temperatures as higher energy molecules escape through the surface tension at the water/air interface. A net loss of water can only happen if the humidity of the air is below 100% saturation with water vapour, however.

In the case where the humidity is 100% the number of water vapour molecules leaving the water puddle, or whatever, is balanced by an equal number entering, so the net result is no change in the amount of water in spite of evaporation occurring.

When you heat water up the percentage of high energy water molecules increases until the rate of evaporation/loss of high energy molecules is so great the water cannot get any hotter, because so much energy is being lost to it. This is its boiling point.

Answer 3

Nature wants and needs to be in equilibrium. When the humidity is less than 100%, all water puddles will evaporate to equalize the effect that the air contains less water than the puddles. Water evaporates faster on warm day or by boiling it is because the available heat energy makes water molecules move faster and therefore easier to escape into the air. Therefore water doesn't need to be boiled to 100 degree C to evaporate, as long as there is a difference in humidity (air and puddles of water), water will dries up, evaporates.

Answer 4

At any temperature water is in equillibrium with water vapour above the surface. There is a maximum amount of water vapour that air can contain at any given temperature. It is then said to be saturated. If the air above the puddle contains less than that, then the puddle evaporates until the air is saturated. The puddle stops evaporating then - except the wind blows that lot of air away and some fresh, unsaturated air replaces it.
I thought this was simple until I tried to explain it!

Answer 5

Its simple. In the water, there are billions of molecules bouncing around. There AVERAGE temperature may be 75degrees. But some aren't moving at all and some are moving faster. Sometimes, one randomly gets enough speed to break through the surface (surface tension) and escapes. Thats why you feel cooler when water is on you. All of the high energy molecules evaporate away, leaving the remaining water a little cooler.

Answer 6

Water has a finite vapor pressure at any temperature. It is about 0.065 atmospheres at 37 C, less at lower temperatures, and increases to 1 atmosphere at 100 C. Since a puddle has no mechanism for retaining water that goes into vapor phase, the water will eventually all evaporate.

Answer 7

Reading other people's answers I saw that everyone explained the water vapor concept pretty well. Another important thing regarding temperature is that temperature is directly related to the kinetic energy of the substance's molecules. For general purposes, the temperature of water is ONLY dependent on its internal energy, which is in turn dependent on the water molecules' kinetic energy. Thus, at higher temperatures the water molecules have higher kinetic energy and more of them have velocities greater than the escape velocity, which is the speed needed to escape the intermolecular forces (in this case, H-bonds) of other water molecules. This, in conjunction with how much water is in the air (see people's vapor comments), contributes to evaporation.

Answer 8

The boiling point is just the temperature at which the vapor pressure of the liquid is equal to that of the atmosphere. Water has a vapor pressure at lower temperatures, and is always evaporating, just at a slower rate.

Answer 9

Evapouration is not the same as boiling. Water will evapourate whenever the relative humidity of the air is less than its vapour saturation point. Air at any temperature can hold a certain amount of water vapour (warm air holds more than cold air). If the air above the puddle has less water vapour than it can hold based on its temperature, the water in the puddle will evapourate.

Answer 10

Evaporation is not the same as boiling. There will always be some water in the air (hence the relative humidity), due to the water vapor pressure. Provide more heat, and air can take more water as a "solution" (humidity is just that: water that "dissolved" away in air, as salt dissolves in water).

Boiling water is like heating salt until it melts (to keep with the water/air, salt/water analogy).