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Specific Heat

  1. Nov 4, 2013 #1
    1. The problem statement, all variables and given/known data
    Large beds of rock are used in some solar-heated homes to store heat. Assume that the specific heat of the rocks is 0.82 J/g-K. (a) Calculate the quantity of heat absorbed by 50.0 kg of rocks if their temperature increases by 12.0°C. (b) What temperature change would these rocks undergo if they emitted 450 kJ of heat?


    2. Relevant equations

    Cs=[itex]\frac{q}{m * ΔT}[/itex]

    3. The attempt at a solution

    For part a, I have rearranged the formula to give me q=Cs X m X ΔT, and got an answer of 4.9*105 J. Part B, however, all I could think to do was try and rearrange the equation again by solving for ΔT. Either I cannot figure out how to rearrange it (this is probably the case, I was never very good at that), or I am on the wrong track completely. Either way, I'm probably also over-thinking it.

    Also, a question about forum rules, I am studying for a test that is tomorrow afternoon and will probably have several other questions tonight on a variety of subjects (such as ΔH, electron config, net ionic equations, concentrations of solutions/molarity etc). Am I allowed to create a new thread for each question or should I stick to this thread?

    Thanks for the help.
     
  2. jcsd
  3. Nov 4, 2013 #2

    tiny-tim

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    Hi FTCC.student! :smile:
    Should work.

    Show us how far you got.
    yes :smile:

    quick! :wink:
     
  4. Nov 4, 2013 #3
    Well okay, this is what I got when I tried to solve for delta-T (I tried twice and did something wrong, I can't remember how to isolate it because it is in the denominator...) the -x- represents that variable being cancelled.


    ΔT = [itex]\frac{Cs*m}{q}[/itex]

    Which gave me: ΔT=(0.82 J/g-K)(50.0g)/450kJ

    That answer was far from correct. I also tried multiplying all my given variables, also far from correct :(

    So what I'm really confused on here probably isnt the actual chemistry portion, just how to rearrange the dang formula
     
  5. Nov 4, 2013 #4

    haruspex

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    (Your LaTex was messed up because you used "" inside [itex]. That doesn't work. You have to use _ for subscript, ^ for superscript, etc.)
    Let's try that one step at a time:
    Cs=[itex]\frac{q}{m * ΔT}[/itex]​
    Multiply both sides by ΔT
    ΔT*Cs=[itex]\frac{q}{m}[/itex]​
    What next?
     
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