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Converting Celsius to Kelvin Easy but slightly confusing

  1. Nov 6, 2008 #1
    1. The problem statement, all variables and given/known data

    I'm doing calorimetry, and I have 34.73C and 63C. I need to subtract 63 from 34.73, and get the answer in Kelvin.

    2. Relevant equations
    3. The attempt at a solution

    I know you add 273 to Celsius values to get Kelvin, but I am not sure which of these methods is correct:

    1. (34.73C+273) - (63C+273) = -28.27K
    2. 34.73C-63C = -28.27C. Then, -28.27C + 273 = 244.73K

    Which one is the correct method? The first one seems unlikely just because the Kelvin's are essentially canceled out in the equation..
    Last edited: Nov 6, 2008
  2. jcsd
  3. Nov 6, 2008 #2


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    Staff Emeritus
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    The first one. You are subtracting one temperature from another so the "base"- that is what temperature corresponds to 0- is irrelevant. You could as easily have just said that 34.73- 63= -28.27 degrees. Since 1 degree Celcius is the same "size" as 1 degree Kelvin, the difference is the same in both systems.
  4. Nov 6, 2008 #3
    Ah I just realized that I was calculating the DECREASE in temperature of hot water, so a negative decrease is a positive value. Thanks!
    Last edited: Nov 6, 2008
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