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Help with temperature and Pressure!

  1. Nov 3, 2009 #1
    Ok, please could somebody give me some guidence on how to answer this question!

    An air bed is pumped up and left on the beach on a warm day. The pressure of the air in the air bed is 105 kPa when the temperature is 17 degrees c. What is the pressure when the temperature on the beach has risen to 37 degrees c.

    Many thanks in advance for your help!
     
  2. jcsd
  3. Nov 3, 2009 #2

    kuruman

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    Hi hippyhoppy, welcome to PF. Please use the homework template when post here and show the relevant equations and some attempt towards the solution of the problem.

    So what equation do you think is relevant here?
     
  4. Nov 3, 2009 #3
    Sorry about that! Im not really too sure - this is what i was stuck on, the only thing i could think of is PV=nRT but i dont see how its relevant
     
  5. Nov 3, 2009 #4

    kuruman

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    The ideal gas law is extremely relevant. As the balloon heats up, which of the five quantities that appear in the gas law remain constant and which change?
     
  6. Nov 3, 2009 #5
    Temperature changes?
    Sorry im not sure about velocity...
    n stays the same
    R will stay constant
     
  7. Nov 3, 2009 #6

    kuruman

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    pV n R T

    p = pressure
    V = volume (not velocity)
    n = number of moles in the gas
    R = Universal Gas Constant
    T = Temperature

    Let's try one more time. Five quantities as listed above. Which ones change and which ones remain constant? Imagine the balloon lying on the hot sand.
     
  8. Nov 3, 2009 #7
    Sorry, physics isnt my strong Point! Ok, The pressure increases as it always does with temperature as with p/t= constant right? Again, volume im not too sure but i would guess that the voulume would stay the same. Im fairly sure the number of moles will stay the same, to be honest ive never been taught the Universal Gas Constant, so wouldnt know and the temperature is increasing. Sorry i dont know much.
     
  9. Nov 3, 2009 #8

    kuruman

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    You are doing fine. R is constant, that's why it is called that, n the number of moles will change only if gas entered or left the balloon (which it does not) and the volume cannot appreciably change when the temperature changes only by 20 degrees.

    So you are correct in saying p/T = constant. This means that pressure divided by temperature when the temperature is 17 Celsius is the same as pressure divided by temperature when the temperature is 37 degrees Celsius. Can you say this with an equation and put in some numbers? Don't forget to convert the temperature from Celsius to Kelvin.
     
  10. Nov 3, 2009 #9
    Sorry i am confused! Do you mean that i put the equation like this:

    105/37? Sorry you must be getting annoyed!
     
  11. Nov 3, 2009 #10

    kuruman

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    As long as you are trying your best, I will not get annoyed.

    105 kPa = 105x103 Pa
    17 oC = 273+17 = 290 K

    One side of the p/T equation then is

    105x103 / 290

    What do you think the other side of the equation should be?
     
  12. Nov 3, 2009 #11
    Sorry im confused as to which equation.

    p/t=constant or PV=nRT

    Sorry, i get the Kelvin and Pa Part
     
  13. Nov 3, 2009 #12
    Can anyone help please!!
     
  14. Nov 3, 2009 #13

    kuruman

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    p/T = constant
     
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