Small issue regarding the wording of a thermodynamics question

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Homework Help Overview

The discussion revolves around a thermodynamics question, specifically addressing the wording of a problem related to changes in internal energy. Participants are examining the implications of the term 'increase' in the context of the first law of thermodynamics.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants are questioning the appropriateness of the term 'increase' in the problem statement, suggesting it may need to be 'decrease' or 'change'. There is a debate about the interpretation of the internal energy change based on the calculated values and the definitions involved.

Discussion Status

The discussion is ongoing, with participants expressing differing views on the wording of the problem and its implications. Some have provided calculations and reasoning to support their positions, while others are exploring the compatibility of the given data with thermodynamic principles.

Contextual Notes

There is mention of specific values related to work done and heat removed, as well as references to the behavior of ideal gases under thermodynamic equilibrium conditions. The calculations presented raise questions about the consistency of the problem statement with established thermodynamic equations.

dregozo

Homework Statement


upload_2018-1-3_20-54-8.png


The issue is the word 'increase' in c)iii), where I'm pretty sure the wording should have been 'decrease' or at least 'change', since both the work done and the heat removed have a negative value.

Homework Equations


dU = dQ + dW (1st law)

The Attempt at a Solution


My answer to c)iii) was -160J.
 

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dregozo said:
The issue is the word 'increase' in c)iii), where I'm pretty sure the wording should have been 'decrease' or at least 'change', since both the work done and the heat removed have a negative value.
"Increase" IS change; don't get your knickers in a knot.
 
Can't agree with you there, an answer of -160J can't possibly suit the description of an INCREASE in internal energy!
 
Something seems very wrong with this problem statement. If the initial and final states of the system are thermodynamic equilibrium states for an ideal gas, then we must have that $$\Delta (PV)=nR\Delta T$$ and
$$\Delta U=nC_v\Delta T$$Combining these two equations gives:$$\Delta U=\frac{C_v}{R}\Delta (PV)$$For a monoatomic ideal gas the ratio of the heat capacity to the gas constant is 1.5, and for a diatomic gas, it is 2.5. From the data given in the table, $$\Delta (PV)=-5\ J$$This doesn't seem compatible with the change of -160 J calculated from the work and the heat removed. Thoughts?
 

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