Calculate Work (w) for Isothermal Gas Expansion/Compression

Click For Summary

Homework Help Overview

The discussion revolves around calculating the work done during the isothermal expansion or compression of an ideal gas, specifically involving an initial volume of 6.5L and a final volume of 34.3L at a given pressure. The context includes the application of the ideal gas law and the work formula for isothermal processes.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants explore the relationship between pressure and volume in the context of the ideal gas law and question how to apply the work formula given the lack of certain variables like moles and temperature. There is discussion about substituting values into the work equation and whether to use initial or final states for pressure and volume.

Discussion Status

Participants are actively engaging with the problem, clarifying the use of the ideal gas law and the implications of isothermal conditions. Some guidance has been provided regarding the constancy of nRT during the process, but there is still exploration of how to apply this to the calculation of work.

Contextual Notes

There is a noted lack of information regarding the number of moles and temperature, which are crucial for calculating work in this context. Participants are also considering the boundaries between chemistry and physics in their approach to the problem.

IoFawkes
Messages
3
Reaction score
2

Homework Statement


Calculate Work(w) when 6.5L of an ideal gas at an initial pressure of 34.3atm is expanded or compressed isothermally to a final volume of 34.3L reversibly. Answer in J

Homework Equations


PV=nRT
P1V1=P2V2
w=-nRT In(V2/V1)

The Attempt at a Solution


Using w=-nRT In(V2/V1)
I'm not given mols or T, I know T=constant, since it's isothermal
Can I use PV=nRT and substitute (PV) in for (nRT) in the equation: w=-nRT In(V2/V1) ?
If so, what should I use for values of P and V? Final/Initial/delta?

Io

PS: This may be in the wrong place, the boundary seems unclear in Chem/Phys or Phys/Chem studies.
 
Physics news on Phys.org
Welcome to PF!
IoFawkes said:
Can I use PV=nRT and substitute (PV) in for (nRT) in the equation: w=-nRT In(V2/V1) ?
Yes
If so, what should I use for values of P and V? Final/Initial/delta?
How does PV in the initial state compare to PV in the final state?
 
  • Like
Likes   Reactions: IoFawkes
TSny said:
How does PV in the initial state compare to PV in the final state?
P1V1=P2V2 so it doesn't matter which I use as long as P and V are both initial values, or final values. Correct?
EDIT: Except it's asking for work done, so would it be the Change in Pressure and Volume?
Io
 
Last edited:
IoFawkes said:
P1V1=P2V2 so it doesn't matter which I use as long as P and V are both initial values, or final values. Correct?
Yes
EDIT: Except it's asking for work done, so would it be the Change in Pressure and Volume?
nRT is a constant for an isothermal process. At any point along the process, nRT has the same value. The ideal gas law tells us that for any state, nRT = PV. So, nRT for the isothermal process equals PV evaluated for any state along the isothermal process.

nRT would not correspond to a change in PV.
 
  • Like
Likes   Reactions: IoFawkes
TSny said:
nRT is a constant for an isothermal process. At any point along the process, nRT has the same value. The ideal gas law tells us that for any state, nRT = PV. So, nRT for the isothermal process equals PV evaluated for any state along the isothermal process.

nRT would not correspond to a change in PV.

Ah, that makes sense, thanks! How wonderful a change in perspective.

Io
 

Similar threads

Confusion about work done by a gas - Thermodynamics
  • · Replies 15 ·
Replies
15
Views
2K
Reversible Isothermal Expansion Steam
  • · Replies 2 ·
Replies
2
Views
3K
Thermodynamics Work from pressure
  • · Replies 4 ·
Replies
4
Views
2K
Work Done by Gas in Isothermal Expansion of Balloon
  • · Replies 5 ·
Replies
5
Views
8K
Work done in adiabatic process vs work done in isothermal
  • · Replies 2 ·
Replies
2
Views
3K
Thermal efficiency of the engine in a PV diagram
  • · Replies 2 ·
Replies
2
Views
3K
Efficiency of Stirling Cycle - Is it the same as the Carnot Engine?
  • · Replies 14 ·
Replies
14
Views
2K
Is My Calculation for Bicycle Pump Pressure Incorrect?
  • · Replies 116 ·
4
Replies
116
Views
7K
To find total work done from multiple reversible processes
  • · Replies 3 ·
Replies
3
Views
2K
Is PV^gamma Constant in Adiabatic Processes?
  • · Replies 9 ·
Replies
9
Views
6K