Why is there water on a cold bottle?

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In summary, condensation occurs when the air next to a cold object is cooled and is unable to hold as much water vapor, causing some of it to condense onto the object's surface. This phenomenon can occur with any cold object, but is more noticeable with a bottle of water due to its ability to keep its surface cool. The amount of water vapor in the air increases with temperature, but can condense out if the humidity is high. Water acts like a gas because it has a vapour pressure at temperatures below its boiling point. Even in a closed box with no external pressure, there will still be water vapour present. The time it takes to reach equilibrium depends on the volume of the box and the temperature.
  • #1
Raz91
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Hello ,

I was always wondering about this phenomenon :

when i take out a cold bottle from the refrigerator , after a few seconds (lets say at room temperature) the bottle is surrounded by water.

the question is - why is it? where did the water come from ?
is it should happen with any cold body ?

(feel free to speak high phycis )

thank u !
 
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  • #2
There's some amount of water vapor floating around in the room air. The air next to the cold bottle is cooled by the bottle, and when it cools some of that water vapor condenses onto the bottle.

Any cold object will do the trick, but a bottle of water is particularly good at keeping its surface cool (because as the surface warms, water circulation brings more cold water from deep inside the bottle to the edge) so you may get a more pronounced effect with a bottle of water than, for example, an apple.
 
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  • #3
Note that the amount of water that can be held in the air increases with the temperature of the air. Since the air is, as Nugatory says, cooled by the bottle the amount of water that it can hold is reduced. If the humidity (amount of water already in the air) it high the water will condense out of the air.
 
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HallsofIvy said:
Note that the amount of water that can be held in the air increases with the temperature of the air. Since the air is, as Nugatory says, cooled by the bottle the amount of water that it can hold is reduced. If the humidity (amount of water already in the air) it high the water will condense out of the air.

That expression is a bit misleading but it's commonly used. In fact, it's all a matter of partial pressures. Air isn't a sponge (although that's what it seems). The maximum proportion of water vapour in the air is totally due to the vapour pressure at the ambient temperature. You would get exactly the same amount of water vapour in a container if the container were evacuated and then the pressure allowed to increase as water evaporates off a water surface. The equilibrium situation would always involve 'saturated' air (there- I've done it myself!)
 
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  • #5
so I have another question - what makes the water act like a gas ? I know that the evaporation temp. at room pressure is ~ 100 C , so if the temperture is < 100 and the pressure is ~ 1 atm why the water are gas?

thank you
 
  • #6
Raz91 said:
so I have another question - what makes the water act like a gas ? I know that the evaporation temp. at room pressure is ~ 100 C , so if the temperture is < 100 and the pressure is ~ 1 atm why the water are gas?

thank you

There is still a pressure of vapour from the water surface at temperatures less than 100C. The reason that boiling occurs is that the vapour pressure at 100C is equal to atmospheric. Up on a mountain top, water will boil rapidly in the low 90s (Hopeless for cooking) but, in a pressure cooker, the water will boil at a higher temperature.
Below boiling point, there is a constant exchange of molecules of and onto the surface. Don't confuse the equilibrium situation (in closed box after a long time) with what happens when there is a constant supply of fresh air over the surface.
 
  • #7
so let's say I take a glass of water and put it in a closed box ( vacccum)- there will be no vapours?
 
  • #8
There will be vapour with a pressure appropriate to the temperature in the box. The time taken to reach equilibrium will depend on the volume of the box and the temperature.
 
  • #9
Perhaps think of "the temperature of the water" as representing the average velocity of the water molecules. There will always be some that are moving faster then average and some will be fast enough to escape the surface forming water vapour. If the box is sealed the vapour pressure rises until there is an equal flow back the other way and an equilibrium is reached.
 

1. Why does a cold bottle sweat?

When a cold bottle is taken out of a refrigerator or cooler, it will often have droplets of water on the outside of the bottle. This is known as sweating. The main reason for this is due to condensation.

2. What is condensation and how does it relate to a cold bottle sweating?

Condensation is the process of a gas turning into a liquid. In this case, the gas is water vapor from the air. When the cold bottle is taken out of a cooler, the cold surface of the bottle causes the water vapor in the air to cool and turn into liquid, resulting in the droplets of water on the outside of the bottle.

3. Does the type of material the bottle is made of affect how much it sweats?

Yes, the type of material can affect how much a bottle sweats. Materials that are poor conductors of heat, such as plastic, tend to sweat more because they do not transfer the cold temperature as quickly as materials such as glass or metal. This means that the surface of the bottle stays cold for longer, causing more condensation to occur.

4. Is there a way to prevent a cold bottle from sweating?

One way to prevent a cold bottle from sweating is to use an insulating material, such as a koozie or a towel wrapped around the bottle. This will help keep the surface of the bottle warmer and prevent condensation from occurring. Another way is to let the bottle sit at room temperature for a few minutes before opening it, as this will allow the bottle to adjust to the temperature of the room and reduce the amount of condensation.

5. Are there any other factors that can contribute to a cold bottle sweating?

Other factors that can contribute to a cold bottle sweating include the humidity level in the air and the temperature difference between the inside and outside of the bottle. In areas with high humidity, there will be more water vapor in the air, increasing the likelihood of condensation. Additionally, a larger temperature difference between the inside and outside of the bottle will also lead to more sweating.

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