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  1. #1

    md journeymans practice test

    i am trying to find a formula to figure out a practice question for a study guide and the question is how many btus must be added to one pound of ice at 32 degrees fahrenheit at sea level to change the entire pound of ice to one pound of water at the same temp. I know there is a formula just cant remember it can anyone help.

  2. #2
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  3. #3
    Join Date
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    Latent Heat of Fusion = 144 BTUs/Lb. The Latent Heat of Fusion refers to a change of state from water to ice, or vice versa. No temperature change.

  4. #4
    Join Date
    Jan 2007
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    Josh, it's not a formula it's a constant that you are going to have to memorize. the magic number is 144 BTU/lb. Water to steam is 970 BTU/lb. Try to memorize these among the few dozen others that you are going to run into though out your career. Thats what's great about this sight is when you forget something either ask or check out the educational areas and it's in here somewhere.
    ckartson
    I didn't write the book I just read it!

  5. #5
    Join Date
    Jan 2007
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    Figure 2-9 in the link that Dlove provides has a nice graphical chart! If you haven't seen it already.
    ckartson
    I didn't write the book I just read it!

  6. #6
    Join Date
    Feb 2012
    Location
    VA
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    Ice changes to water at 32 F and atmospheric pressur. Heat of absorption to produce this change is 144 Btu/lb thats per lb .

    The equation for changing ice to water is
    Heat= wt. Of ice x sp. Ht. Capacity of ice x temperture change.

    The heat will be in btu. The (wt) will be in pounds
    Spcific heat will be in btu/lb. ( the specific heat of water is 1 btu/lb.
    The specific heat of ice is 0.50 Btu/lb.)

  7. #7
    Join Date
    Feb 2012
    Location
    VA
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    Example : how many btu will be absorbed in changing 25lb. Of ice at 5F to water at 40F.

    Raise the temperture of ice 5F to 32F

    Btu=wt. Of ice x sp. Ht. Capacity of ice x temperture change.

    Btu= 25x0.50 x ( 32-5)
    Btu= 25x 0. 50 x 27
    Btu= 337.5 btu.

    To melt ice at 32F
    Btu = wt. Of ice x latent heat of fusion of ice .
    Btu= 25 x 144 .
    Btu = 3600

    To warm water from 32F to 40F .

    Btu= wt. Of water x sp. Ht. Capacity of water x the temperture change

  8. #8
    Join Date
    Feb 2012
    Location
    VA
    Posts
    109
    Lets finish
    Btu = 25x1 x (40- 32 )
    Btu= 25 x 1 x 8
    Btu= 200 Btu

    Total heat required to change 25lb. Of ice to water at 40F :
    Btu= 337.5 + 3600 + 200 = 4137.5 Btu

    Now this excersise should help you with your test good luck

  9. #9

    Maryland journeymens practice test

    Thanks for the help I was making the question harder then it had to be and that's why this site is great thanks again to all who answered my question

  10. #10
    Join Date
    Mar 2012
    Location
    Connecticut
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    43
    Quote Originally Posted by dlove View Post
    Thank you for the website.

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