Molekylerne nær overfladen har en sandsynlighed for at forlade væsken. Molekylet skal overvinde den modstand, som overfladespændingen giver. De fleste molekyler afvises og forbliver i væsken fordi hastigheden ikke var stor nok, men nogle af dem forlader væsken pga molekylets hastighed.
Hastigheden af molekylerne kan antages at være normalfordelt, så selv ved stuetemperatur har en lille andel af molekylerne en høj nok hastigheder til at kunne bryde igennem overfladen og "fordampe" ud. Sandsynlighedsfordelingen afhænger af temperaturen. Eksempelvis vil 100% af molekylerne i vand fordampe ved over 100 grader celcius ved 1 bars tryk. Det er derfor man ikke kan varme vand op til mere end 100C ved 1 bars tryk (normalt atmosfærisk tryk).
En sjat væske, som har en større overflade vil have flere molekyler nær overfladen (da den er større). Jo flere molekyler, jo flere vil forlade væsken per sekund.
Derfor fordamper en sjat vand i en lav, flad skål hurtigere end i et højt, smalt glas (pga den større overflade, som giver flere molekyler placeret i den zone, hvor de kan forlade væsken (fordampe)).
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#1 tusind tak fidusen :)
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#3 Hmm har ikke rigtigt noget svar, jeg søgte en måde at løse gåden på :P men lads sige svaret er 3 :)
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Bare for at forklare endnu mere (taget fra wiki)
1. Concentration of the substance evaporating in the air
If the air already has a high concentration of the substance evaporating, then the given substance will evaporate more slowly.
2. Concentration of other substances in the air
If the air is already saturated with other substances, it can have a lower capacity for the substance evaporating.
3. Flow rate of air
This is in part related to the concentration points above. If fresh air is moving over the substance all the time, then the concentration of the substance in the air is less likely to go up with time, thus encouraging faster evaporation. This is the result of the boundary layer at the evaporation surface decreasing with flow velocity, decreasing the diffusion distance in the stagnant layer.
4. Inter-molecular forces
The stronger the forces keeping the molecules together in the liquid state, the more energy one must get to escape. This is characterized by the enthalpy of vaporization.
5. Pressure
Evaporation happens faster if there is less exertion on the surface keeping the molecules from launching themselves.
6. Surface area
A substance that has a larger surface area will evaporate faster, as there are more surface molecules that are able to escape.
7. Temperature of the substance
If the substance is hotter, then its molecules have a higher average kinetic energy, and evaporation will be faster.
8. Density
The higher the density the slower a liquid evaporates.
Og som #1 har forklaret passer dit eksperiment godt ind :)
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