Solve Thermo Probs: Part A of PV=mRT w/ Figure

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Discussion Overview

The discussion revolves around solving part A of a thermodynamics problem involving the Ideal Gas Law, specifically the equation PV = mRT. Participants are focused on determining the pressure needed to calculate temperature from the given volume and other parameters, as illustrated in a provided figure.

Discussion Character

  • Homework-related
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant calculates the volume of state 2 as half of state 1 and seeks to find the pressure to use in the Ideal Gas Law.
  • Another participant questions how the pressure arises initially and suggests connecting a property of the piston to the pressure.
  • A participant proposes that the pressure remains constant throughout states 1 and 2 due to the weight of the piston and atmospheric pressure being unchanged.
  • There is a clarification regarding whether the piston exerts a force on the air, with a later edit acknowledging that the pressure does not change because of constant external factors.

Areas of Agreement / Disagreement

Participants express uncertainty regarding the relationship between the piston and pressure, with some agreeing that pressure remains constant while others seek further clarification on the mechanics involved. The discussion does not reach a consensus on the best approach to find the pressure.

Contextual Notes

Assumptions about the system, such as the behavior of the piston and the effects of atmospheric pressure, are not fully explored, leaving some aspects of the problem unresolved.

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Homework Statement


[PLAIN]http://img821.imageshack.us/img821/8541/cheme.png

I am only looking for help in part a.

Homework Equations



PV = mRT


The Attempt at a Solution



By looking at the figure, I was able to calculate the volume of state 2, which is half of the volume of state 1.

V1 = (mRT1)/P1
V1 = (5*0.287*573)/200
V1 = 4.11 meters cubed

V2 = V1/2
V2 = 2.06 meters cubed

However, in order to calculate the temperature by using the Ideal Gas Law, I need pressure first. How do I go about finding pressure? Is there an assumption I'm supposed to make first?
 
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How does the pressure arise initially? Can you connect a property of the piston to the pressure?
 
Mapes said:
How does the pressure arise initially? Can you connect a property of the piston to the pressure?

Well, I guess that since the piston does not exert a force on the air, the pressure stays the same throughout state 1 and 2?

Edit: Actually, the pressure arises from the weight of the piston and the atmospheric pressure. So since those two factors stay the same, the pressure is constant throughout states 1 and 2?
 
Last edited:
The piston doesn't exert a force on the air? Or the piston exerts a constant force regardless of its height?
 
Mapes said:
The piston doesn't exert a force on the air? Or the piston exerts a constant force regardless of its height?

Yeah I edited my post, because I realized that since the atmospheric pressure and the weight of the piston are constant, the pressure doesn't change from state 1 to state 2. Thanks for the help.
 

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