Specific Heat

  • #1

Homework Statement


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?


Homework Equations



Cs=[itex]\frac{q}{m * ΔT}[/itex]

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.
 

Answers and Replies

  • #2
tiny-tim
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Hi FTCC.student! :smile:
(b) What temperature change would these rocks undergo if they emitted 450 kJ of heat?

Part B, however, all I could think to do was try and rearrange the equation again by solving for ΔT.

Should work.

Show us how far you got.
… Am I allowed to create a new thread for each question …

yes :smile:

quick! :wink:
 
  • #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
 
  • #4
haruspex
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ΔT = [itex]\frac{C_s*m}{q}[/itex]
(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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