Thermodynamics-Pressure problem

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Discussion Overview

The discussion revolves around a thermodynamics problem involving a piston-cylinder system undergoing an isobaric process. Participants are tasked with finding the final volume of the cylinder after a specified amount of work is done by the piston, given initial conditions such as pressure, volume, and temperature.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • One participant presents the problem statement and expresses difficulty in determining the correct formulas to solve for the final volume.
  • Another participant emphasizes the definition of an isobaric process and suggests determining an equation for the work done by the piston.
  • Further contributions clarify the relationship between work, force, and displacement, and introduce the concept of pressure as force per area.
  • Participants discuss the integration of pressure with respect to volume to find the work done during the isobaric process.
  • There is a back-and-forth regarding how to approach the calculation of work without knowing the change in volume initially.
  • Eventually, one participant provides a calculated final volume, but later retracts it in favor of a different value.

Areas of Agreement / Disagreement

The discussion shows a progression of ideas and calculations, but there is no consensus on the final volume as one participant changes their answer. The approach to solving the problem is discussed, but uncertainty remains regarding the correct application of formulas and the final result.

Contextual Notes

Participants express uncertainty about the integration process and the relationship between work and volume change, indicating potential limitations in their understanding of the problem's requirements.

Who May Find This Useful

This discussion may be useful for students studying thermodynamics, particularly those working on problems involving isobaric processes and the calculation of work done by gases in piston-cylinder systems.

jakeward46
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Homework Statement



A piston cylinder with a diameter of 25cm and an initial volume V1 of 10litres, contains air at pressure P1 of 650kPa and a temp T1 of 300K, an Isobaric process pccurs and the piston delivers 10kJ of work.
Find the final volume V2 of the piston/cylinder in litres.

Homework Equations





The Attempt at a Solution



Ive tried using all different types of forumlas in different orders but i cannot come up with a reasonable answer, if someone could tell me the correct formulas to start the solution, that would be much appriciated.
 
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Think of the definition of "isobaric." Also, can you determine an equation for the work done by the piston?
 
edgepflow said:
Think of the definition of "isobaric." Also, can you determine an equation for the work done by the piston?

well , W= F.d but i probably cannot use that without first working out for other info. The isobaric, constant pressure,
 
OK, now let's go a step further.

Yes, dW = F dx or W = Integral (F dx)

Now consider the definition of Pressure: Pressure = Force / Area.

Can you update the work formula with pressure?
 
edgepflow said:
OK, now let's go a step further.

Yes, dW = F dx or W = Integral (F dx)

Now consider the definition of Pressure: Pressure = Force / Area.

Can you update the work formula with pressure?

Ok, dW = P.dV --> W=P.dV
 
That is good.

Now since the process is isobaric (constant pressure),

what is the value of W = Integral (P dV)?
 
edgepflow said:
That is good.

Now since the process is isobaric (constant pressure),

what is the value of W = Integral (P dV)?

how can i get the value of W when i do not have the difference in volume
 
jakeward46 said:
how can i get the value of W when i do not have the difference in volume
Recall the problem statement: they give you the work and ask you to find the final volume. So for constant P, what is the integral of P dV? Integrate from V1 to V2 for constant P.
 
Last edited:
Ok will have a go, not to sure though, thanks
 
  • #10
V2=9.9846 litres!
 
  • #11
Scrap that,V2=25.4 litres
 

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