Work done by gas expanding into a cylinder+piston system

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Homework Help Overview

The discussion revolves around the work done by a gas expanding in a cylinder-piston system, comparing two scenarios: one where the expansion is quasi-static and another where it is rapid. Participants are exploring the implications of these different conditions on the work calculated.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • Participants are examining the differences in work calculations for two scenarios of gas expansion, questioning why the rapid expansion (B) might yield a different result from the quasi-static expansion (A). There is a focus on the assumptions regarding the nature of the expansion and the conditions under which the work is calculated.

Discussion Status

Some participants are seeking clarification on the reasoning behind the differing approaches to calculating work in the two scenarios. There is an acknowledgment of potential differences in the paths taken in PV space, though no consensus has been reached regarding the implications of these differences.

Contextual Notes

Participants are considering the implications of the gas expanding into the atmosphere versus a piston system, and how this affects the assumptions about the nature of the work done. There is uncertainty about whether the work done in both scenarios could be the same despite the different conditions.

LCSphysicist
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Homework Statement
A thin-walled metal container of volume V contains a gas at high pressure.
Connected to the container is a capillary tube and stopcock. When the stopcock is
opened slightly, the gas leaks slowly into a cylinder equipped with a nonleaking,
frictionless piston, where the pressure remains constant at the atmospheric value $P_0$.
(a) Show that, after as much gas as possible has leaked out, an amount of work $P_0(V_0-V)$
has been done, where $V_0$ is the volume of the gas at atmospheric pressure and
temperature.
(b) How much work would be done if the gas leaked directly into the atmosphere?
Relevant Equations
.
I will summarize briefly my reasoning for both letters, since the answer is immediately after that:

A) The work is quasi-static, and the pressure is approximatelly constant and equal to the atmospheric pressure, so the works is $$W = -p\int dV = -p_{0} (V_{0}-V)$$
B) The work is fast, fast enough that no heat flows thought the gas, so that the work is $$W = -\int p dV = -\int_{V_i}^{V_f} p_i (V_i)^{\gamma} dV /V^{\gamma}$$ $$ P_i V_i^{\gamma} / P_o = V_f ^{\gamma}$$

What do you think? I am almost sure it is wrong, so i am posting here to get any help on letter b
 
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If your system is the gas, why do you feel that the answer to B is different from A?
 
Chestermiller said:
If your system is the gas, why do you feel that the answer to B is different from A?
As i said, because the first one "leaks slowly", and nothing has been said about the second one, so i suppose it is more "explosive".

I have questioned myself also if the work is the same, but i was not able to argue why it should be. Even so the final points on (PV space) is the same, the path could be different, resulting in different work.
 
The question implies that the gas is still leaking slowly in case B, but into the atmosphere instead of into a cylinder and piston.
 

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