why does dry heat take away humidity?

Discussion in 'Chemistry' started by river, Oct 17, 2011.

  1. river Valued Senior Member

    Messages:
    9,465
    guys

    there is no air conditioning , no water droplets on my windows , never has been

    therefore , I assume H2O goes somewhere , but where ?
     
  2. Google AdSense Guest Advertisement



    to hide all adverts.
  3. billvon Valued Senior Member

    Messages:
    12,755
    Nowhere. It's still there, in your air. But when you warm up the air, the relative humidity goes down - EVEN THOUGH ALL THE WATER IS STILL IN THE AIR. (Important part capitalized.)
     
  4. Google AdSense Guest Advertisement



    to hide all adverts.
  5. Enmos Staff Member

    Messages:
    43,184
    Because it's dry. Cold dry air will take away humidity as well.

    The dry air will not be as dry anymore..
     
  6. Google AdSense Guest Advertisement



    to hide all adverts.
  7. origin Trump is the best argument against a democracy. Valued Senior Member

    Messages:
    9,921
    Are you kidding? Have you looked at the thread? It is very very simple. If you take a volume of air and heat it up the relative humidity drops. That is it in a nut shell. If you don't believe me simply google relative humidity and read the links. It should take you about 15 minutes to understand.
     
  8. arauca Banned Banned

    Messages:
    4,564


    Where toes the water from the moisture air goes ?
    How come during winter the humidity drops in the house ?
     
  9. origin Trump is the best argument against a democracy. Valued Senior Member

    Messages:
    9,921
    It doesn't go anywhere, it stays in the air! Look at the graph below:

    Please Register or Log in to view the hidden image!



    Assume that the temperature is 14C outside and the humidity is 100%. That means that it will be foggy, raining or dew will be forming on surfaces; basically it 'feels' very wet. The graph shows that there is about 10 grams of water in a kilogram of air.

    Now take this air inside and heat it up to 25C there is still 10 grams of water in each kilogram of air, but now the relative humidity is only 50%. You will no longer have the wet 'feel' to the air, it feels quite comfortable.

    Questions?
     
  10. arauca Banned Banned

    Messages:
    4,564
    I get of the graph . The impact on my comfort 100% at lower temp. is equivalent to a lower RH at higher temp.
     
  11. origin Trump is the best argument against a democracy. Valued Senior Member

    Messages:
    9,921
    Yes, if you heat the air the RH will decrease.
     
  12. convivial Registered Senior Member

    Messages:
    107
    When I want to know the air moisture content, I look at dew point. I don't pay any attention to "humidity" unless I'm curious what the dew point-to-temperature ratio makes as a humidity percentage.

    Questions: why does cold air dry out skin, since while there's less moisture in the air, the air's capacity to hold it has also decreased? And will something wet then dry faster at X humidity at a cold temperature than X humidity at a warm temperature?
     
  13. billvon Valued Senior Member

    Messages:
    12,755
    Because your skin warms the air nearest it, making the air near your skin both warmer and lower in relative humidity.
     
  14. wellwisher Banned Banned

    Messages:
    5,160
    Dry heat takes away humidity because of entropy. For entropy to increase, we need energy. The heat in the warm air, provides the energy needed to increase the local water's entropy.

    Entropy is defined, in part, as a spreading out of the energy to assume all possible energy levels. When the air is dry (very little water vapor), there is a lot of room for the entropy of the water vapor to spread out and assume various rotational, vibrational and translational degrees of freedom. This can be modeled with statistical mechanics. As the air becomes saturated, the entropy finally reaches a maximium.
     
  15. origin Trump is the best argument against a democracy. Valued Senior Member

    Messages:
    9,921
    Does this statement actually make sense to you? The local water's entropy? What is that suppose to mean?

    It is? I have never seen any definition of entropy that implies that.

    This does not make any sense. Maybe you could expound a bit and it would make sense, but I don't think so.:shrug:
     
  16. river Valued Senior Member

    Messages:
    9,465

    can anybody do this experiment ?

    just curious

    like to be there

    Please Register or Log in to view the hidden image!

     
  17. origin Trump is the best argument against a democracy. Valued Senior Member

    Messages:
    9,921
    No.
     

Share This Page