Isothermal Process Homework: Calculate Q(in) & Q(out)

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Homework Help Overview

The discussion revolves around calculating heat transfer (Q(in) and Q(out)) in an isothermal process involving an ideal gas. The participants are exploring the relationships between pressure, volume, and temperature, particularly focusing on the ideal gas law and the implications of missing temperature data.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants discuss the use of the ideal gas law and the relationships between variables in an isothermal process. Questions arise about how to determine temperature and the implications of not having it explicitly provided. There is also a consideration of whether the number of moles is known and how that affects the calculations.

Discussion Status

The discussion is ongoing, with participants providing hints and exploring the connections between the variables involved. Some guidance has been offered regarding the ideal gas law and its relevance to the problem, but there is no consensus on how to proceed without the temperature value.

Contextual Notes

There is uncertainty regarding the number of moles and the temperature, which are critical for solving the problem. The participants are questioning the completeness of the information provided in the original problem statement.

aznmaverick
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Homework Statement


Calculate Q(in) and Q(out).


Homework Equations


Specific Heat: Cv = 5/2 R
R = 8.314 J/mol K


The Attempt at a Solution


For the process C-> A, it is an isothermic process but we are not given temperature. The equation to finding the total work done from C->A is nRT ln (Va/Vc). How do I get T in order to solve for nRT ln (Va/Vc)?
 

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aznmaverick said:
How do I get T in order to solve for nRT ln (Va/Vc)?

Hint: is there a constitutive equation for this substance?
 
Mapes said:
Hint: is there a constitutive equation for this substance?

Yes, I got that from Q (from C to A) = Delta U (C to A) + W (C to A) and since Delta U (C to A) = 0, Q (C to A) = W ( C to A).
W (C to A) for an isothermal process is = (Integral from C to A) P dv

Using the formula PV = nRT and solving for P, we get P = nrT/V, so W (C to A) = (Integral from C to A) nRT/V dv, which comes out to be nRT ln v (from C to A). Finally plugging in C and A, we get nRT ln (Va - Vc) = nRT ln (Va/Vc)
 
The value of nRT can be easily calculated even though neither n nor T are known. Know what I mean?
 
Yes, well, n=1 mole, and T is unknown, but we know that its a constant. So we cannot solve for it?
 
How do you know that there's one mole present? Is there more information in the problem statement that you didn't post?

In any case, the ideal gas law connects all these variables together.
 
Mapes said:
How do you know that there's one mole present? Is there more information in the problem statement that you didn't post?

In any case, the ideal gas law connects all these variables together.

Yea, 1 mole was a given. T is still not given. So does that mean there's no 'real answer' to this question w/o T given?
 
If P, V, and n are known for an ideal gas, then T is known.
 
Mapes said:
If P, V, and n are known for an ideal gas, then T is known.

Got it, thanks!
 

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