# What actually we mean when we say "reaching 100% relative humidity and no further evaporation"?

What do we mean by reaching 100% relative humidity? Is that we reach the utmost vapor pressure at that particular temperature of liquid? Or something else.

If I have 2 half filled water bottle, in one I have a comparatively cooler water than other , does both bottle empty space above water contain same amount of water vapor ? Vapor pressure increase by increase in volume of vapor or the more speedy(more collisionđź’Ą) evaporation of water molecule due to high temperature?

I can't understand it, what actually 100% relative humidity means! Does is the maximum amount of vapor air contain at any temperature (like seat fill completely) or it is the reaching point of equilibrium of vapor at a particular temperature where rate of evaporation is equal to rate of condensation and no further vapor it can contains until an new equilibrium is set by changing temperature of liquid?

Relative humidity is a measure of how much moisture is in the air relative to the maximum amount of moisture that the air can actually hold at that pressure and temperature. So 100% relative humidity means that there is as much moisture in the air as it can hold.

Therefore, 100% relative humdity at one pressure and temperature represents a different amount of absolute water vapour compared to 100% relative humidity at another pressure and temperature.

• So relative humidity change with temperature and pressure? Then does it mean in a closed half filled bottle and water at some x°, relative humidity is 100% when vapor pressure of that water temperature reach? Because rate of evaporation = rate of condensation and no further water can be added more?
– user313211
Commented Oct 15, 2021 at 5:26
• @SureshChandraPal Yes, the absolute about of moisture represented by 100% relative humidity changes with pressure and temperature. 100% relative humidity means no more water can evaporate and stay in the air since the air can't hold anymore water. I am not sure if it is the same as water evaporating at the same rate that it condenses at (i.e. that might just be a mathematical interpretation rather than a physical one). Commented Oct 15, 2021 at 16:40
• I would imagine that that if it physical and not just mathematical, then a beaker filled with water in an enclosed tank at 100% relative humidity would eventually result in water moving from within the the beaker to outside the beaker until liquid water levels inside and outside of the beaker were equal. Due to small variations in the air allowing water to evaporate in some places but condense in others (rather than perfectly distributed rates of evaporation and condensation everywhere which would result in something indistinguishable from math and physical. Commented Oct 15, 2021 at 16:46
• So finally ....overall it is ! When vapor pressure of some temperature reach than 100% humidity peak is reach!?? Right no??
– user313211
Commented Oct 15, 2021 at 16:48
• @SureshChandraPal YEs............. Commented Oct 15, 2021 at 16:49