How much heat is transferred during the compression?

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    Compression Heat
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Discussion Overview

The discussion revolves around the calculation of heat transfer during the isothermal compression of copper under varying pressure conditions. Participants explore the implications of an isothermal process, the work done on the material, and discrepancies between personal calculations and textbook answers.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant presents a calculation for heat transfer during isothermal compression, yielding a result of -416 J, which differs from the textbook answer of -139.9 J.
  • Another participant prompts a reflection on the nature of isothermal processes, suggesting that heat must leave the system to maintain constant temperature during compression.
  • A participant mentions a conversation with their professor, who claims the textbook answer is incorrect, citing previous errors in the same text.
  • Work done on the copper during compression is calculated using an integral approach, resulting in 44.3 J.
  • A participant shares their calculation for the change in internal energy, combining their heat transfer and work results to arrive at -372.7 J.

Areas of Agreement / Disagreement

There is no consensus on the correct amount of heat transferred, as participants present differing calculations and opinions on the accuracy of the textbook answer. The discussion remains unresolved regarding the correct values.

Contextual Notes

Participants express uncertainty about the accuracy of the textbook and the calculations involved, indicating potential limitations in the assumptions or methods used in their analyses.

rsd_sosu
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Would Someone check my work please?
Here is the question.
The pressure on 500g of copper is increased reversibly and isothermally from 0 to 5000atm.
Where
density = 8.96X10^3kg/m^3
Volume Expansivity = 49.5X10^-6K^-1
isothermal compressibility = 6.18X10^-12Pa^-1
specific heat = 385 J/Kg*K
temp = 298K

Now the first part of the question ask how much heat is transferred during the compression? (I worked this out but got a different answer than the book )anyway here it is.
Q = -T*V*(Volume Expansivity)*(P_f-P_i)
Q = -(298K)*(5.58X10^-5m^3)*(49.5X10^-6K^-1)*(5.056X10^8Pa)
Where i found Volume From Mass/density
and changed Pressure from atm to Pascals
after pluging in all these numbers my answer is -416 N*m or -416J
the answer the book gives is -139.9J

Can anyone see the problem here?
sorry if there is any confusion with symbols this is my first post and do not know how to use the code yet.
Thanks
 
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"Isothermal process." Ask yourself what is happening in an "isothermal process."
 
Ok I asked my self and I replied the temperature is holding at 298K. What r u getting at? In order for the temp to stay the same heat must leave during compression. Precisely how much is the question being asked.
 


Originally posted by rsd_sosu
Now the first part of the question ask how much heat is transferred during the compression?
How much work is done on the copper as it is compressed?
 
I talked to my Professor today and he informed me that the answer in the book was indeed incorrect. This is not the first time and probably won't be the last error i find. the text i am using is Heat And Thermodynamics by Zemansky and Dittman which is full of errors in the seventh edition. Anyway thanks for the responses.

The Work involved that you (Doc Al) mentioned was in fact the second of four questions asked. Here it is.

[tex] W = \int_{P_i}^{P_f} VkP dP = \frac{1}{2} V k P^2_f[/tex]


[tex] \frac{1}{2}(5.58X10^{-5}m^3)(6.18X10^-^1^2Pa^{-1})(5.07X10^8Pa)^2[/tex]


[tex] = 44.3N-m =44.3J[/tex]

Just to get a bit more practice with this scrip I will show the Change in internal energy as well, which was the third question.

[tex] \Delta U = Q + W = -417J + 44.3J = -372.7J[/tex]

Later,
 
Last edited:

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