science- what causes water to change its liquid form to gas form through evaporation?

Question

does it mean that the surface area absorb heat to 100 C and then gain enough energy to escape from the bond. it sound ridiculous. but otherwise how come they can escape from the bond if they didnt gain energy

Answer 1

No the surface does not heat to 100C. You need to understand the concept of liquid vapor equilibrium (aka vapor pressure).

Any liquid in a closed volume greater than the volume of the liquid will generate a vapor pressure of its molecules in the gas phase. If you apply a vacuum and then reseal, the vapor pressure will rise to a characteristic value for that substance and temperature, and then stay constant. In other words, the liquid-vapor boundary represents a thermodynamic equilibrium between the liquid and gas, with the same number of molecules going from gas-liquid as going liquid-gas.

An open liquid will evaporate depending on the temperature and pressure it is exposed to. If the ambient pressure of the gas is lower than the vapor pressure of the gas, then the liquid will continue evaporating. This is what normally happens to water exposed to dry air. Note that the dew point is the temperature at which water vapor in the air turns to liquid (dew droplets), which is just the reverse of evaporation.

Some real world examples to show you this phenomena: drying your clothes outside. In a very warm and dry climate, the clothes dry much faster. If it is warm and humid, it takes much longer to dry them. A swimming pool loses water every day due to evaporation, and must be refilled in the summer.

At 100C for water, the vapor pressure equals ambient atmospheric pressure, and the water boils. Boiling is just a spontaneous evaporation occurring throughout the liquid, not just at the surface. But 100C is not required for water to evaporate, and some amount of water evaporates at all temperatures.

Every substance has a so-called liquid-vapor-solid (or phase) diagram (temp. vs. pressure) which shows you the temperatures and pressure at which it is liquid and gas.

Finally, evaporation is actually a cooling process, because the higher energy molecules are the ones that evaporate and take the energy with them. The surface from which they evaporate actually is cooled. This is why perspiration cools you off. But when it is humid, the pressure of water vapor in the air is already high, your sweat does evaporate well and drips off.

I hope this does not confuse you too much!

Answer 2

I can assure you that not only will water evaporate at much lower temperature than 100c but will do so at 0C as well. Not only that, but water will do something called sublimation. In the climate here in Minnesota we have water produced from melting snow at temps below freezing at times because the snow-water-ice mixture has salt in it. Evaporation will occur from liquid water at any temp as has been explained by the best answer given above.
I can also attest to the fact that evaporation can occur when snow (ice or solid form of water) is exposed to the sun on days when the temperature is well below freezing. The snow or ice in question will go directly from the solid form to vapor form without ever being liquid. It is impossible under normal conditions for water to be in a liguid form at temps well below freezing.
Go to wikipedia for a detailed answer if you do not believe me.

Answer 3

It's called the Heat of Evaporation. The molecules lose the bond holding them in the liquid state as they gain space between each other from being heated.

Answer 4

Evaporation is the process through which the liquid molecules escape from the surface of the liquid and convert into vapours . So to the whole liquid should be at 100 C to start the evaporation.

Answer 5

at the heat increase molecule in it move faster and faster. The faster it move the more energy it gain to escape from the bond and evaporate.

Answer 6

They can't or look it up on google