1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Doubling Celsius temp also double the pressure?

  1. Nov 30, 2009 #1
    Does doubling the Celsius temp of a container also double the pressure?

    I know it's true for Kelvin but I'm not sure about Celsius.
     
  2. jcsd
  3. Nov 30, 2009 #2

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    No
    Just trying a couple of values should convince you.

    And in you system what would happen to the pressure if you went from 0C to 1C?
     
  4. Nov 30, 2009 #3
    Which equation do I use to figure out if celsius doubles?

    (T2/T1) = (P2/P1)

    Do I use that?
     
  5. Nov 30, 2009 #4

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    Almost, P1/T1=P2/T2=constant.

    But a moments thought about what is double 0C should be enough.

    You should also consider if changing the temperature by the same amount measured in C or F should have the same effect on pressure ?
    Suppose you heat something from body temperature to the boiling point of water.
    In C thats 37 -> 100 = 2.7x
    In F thats 97 -> 212 = 2.2x

    How does the gas molecules know what units you are using ?
     
    Last edited: Nov 30, 2009
  6. Nov 30, 2009 #5
    I still don't understand your explanation mgb
     
  7. Nov 30, 2009 #6

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    The law is that pressure/temperature is constant, doubling temperature doubles pressure.
    I am trying to prove that this only works if you have an absolute 'temperature' ie. one that goes linearly from zero.

    If you have a temperature that doesn't start from absolute zero you get some ridiculous answer, such as increasing the temp from freezing (0C) to 1C would mean an infinite increase in pressure.
    And raising the temperature from body heat to boiling would give a different pressure change depending on what units you used.
    Since these are impossible - it must be that you have to use absolute temperautre.
     
  8. Nov 30, 2009 #7
    Ok thanks mgb...it makes more sense now....but couldnt you also have 0 Kelvin?? So wouldn't an increase from 0K to 1K do the same thing ?
     
    Last edited: Nov 30, 2009
  9. Nov 30, 2009 #8

    ideasrule

    User Avatar
    Homework Helper

    Good point. The solution to the paradox is that we don't normally talk about gases at 1K; most (all?) gases liquefy above that temperature, and the ideal gas law doesn't apply anyways to gases at very low temperatures.

    Think about what happens when a gas, say air, goes from 1 degree Celsius to 2 degrees Celsius. (This is hot enough that the ideal gas law applies, so we're safe in using this thought experiment.) Celsius temperature doubles, but the room in your air doesn't suddenly double in volume when the temperature goes from 1 degree Celsius to 2.
     
  10. Nov 30, 2009 #9
    So we usually talk about Kelvin at around 273K and above which prevents using 0K. Isn't the Kelvin scale directly related to pressure since 0K = 0Pressure? but at zero pressure the celsius scale has a negative value.
     
    Last edited: Nov 30, 2009
  11. Nov 30, 2009 #10

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    Yes that's the whole point of the kelvin scale.
    From 0C to 1C is 274/273 = 0.3% increase in pressure.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Doubling Celsius temp also double the pressure?
  1. Double slits (Replies: 7)

  2. Double slit (Replies: 2)

  3. Double atwood (Replies: 0)

  4. Double the speed (Replies: 3)

  5. Springs Double (Replies: 3)

Loading...