Specific heat capacity and final temperature

  • Thread starter moimoi24
  • Start date
  • #1
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Homework Statement



A 2.8 kg sample of a metal with a specific heat of 0.43KJ/KgC is heated to 100.0C then placed in a 50.0 g sample of water at 30.0C.* What is the final temperature of the metal and the water?


Homework Equations



heat loss by the metal = heat gain by the water

The Attempt at a Solution



I solve it this way:
2800 g x 430 J/gC x (Tf-100) = 50 g x 4.2 J/gC x (Tf - 30)

my final answer is 100 C,

please help me check what makes my answer wrong because the answer on the key is 97C...

Thanks a lot....
 

Answers and Replies

  • #2
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i solve it again and i got 114 as the answer because of 0.43KJ/KgC, it will be 0.43J/gC... Please help me with this one, what makes it wrong?
 
  • #3
ehild
Homework Helper
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1,898

Homework Equations



heat loss by the metal = heat gain by the water

The Attempt at a Solution



I solve it this way:
2800 g x 0.430 J/gC x (Tf-100) = 50 g x 4.2 J/gC x (Tf - 30)
Check the red one. Is it really the heat lost by the metal?


ehild
 
  • #4
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Check the red one. Is it really the heat lost by the metal?


ehild
is it 2800 g x 0.43J/gC x 70 C?
 
  • #5
ehild
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You said that the heat lost by the metal is equal to the heat gained by water.
The metal cools down from 100 C° to Tf, how much heat releases in the cooling process?

ehild
 
  • #6
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You said that the heat lost by the metal is equal to the heat gained by water.
The metal cools down from 100 C° to Tf, how much heat releases in the cooling process?

ehild
i think it should be100C - tf, since there is a decrease in temperature. my answer is 90C, is that correct?
 
  • #7
ehild
Homework Helper
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i think it should be100C - tf, since there is a decrease in temperature. my answer is 90C, is that correct?
Yes, you need to calculate with 100-Tf, but I got different result. Do not drop significant digits during the calculations.

ehild
 

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