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Topic: Need help on amount of heat released  (Read 3093 times)

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Offline oceanmd

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Need help on amount of heat released
« on: March 30, 2008, 09:26:36 PM »
Please check whether I did it right. Is the total amount of heat released a negative number?Thank you very much.

42.3 g of water at 123 degrees C is cooled to solid water at -28 degrees C. What is the total amount of heat released in this process?
q1 = C steam x m x Delta T
q1 = 2.01 x 42.3 x (100-123) = -1955.53
q2 (boiling point) = delta Hcond x m
q2 = -40.7 x 42.3 = -1721.61
q3 = C liquid x m x Delta T
q3 = 4.184 x 42.3 x (0-100) = -17698.32
q4 (freezing point) = delta H solid x m
q4 = -6.01 x 42.3 = -254.223
q5 = C ice x m x delta T
q5 = 2.03 x 42.3 x (-28-0) = -2404.332
q total = -24034

Offline enahs

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Re: Need help on amount of heat released
« Reply #1 on: March 30, 2008, 09:37:37 PM »
I am assuming your numbers and constants are correct. Method looks ok.

Should it be negative? You tell me. To cool steam down, make water, and freeze water, do you have to add energy in the form of the heat to the system, or take it away?


Offline oceanmd

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Re: Need help on amount of heat released
« Reply #2 on: March 30, 2008, 09:43:16 PM »
The energy is released, so it is taken away, so the answer is negative. Got it. Thank you again.

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