Reversible vs. Irreversible

Boltzmann Equation for Entropy:

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905085650
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Joined: Fri Sep 28, 2018 12:19 am

Reversible vs. Irreversible

Postby 905085650 » Sun Feb 10, 2019 10:38 pm

Can someone explain to me why W(reversible) is greater than W(irreversible)? Thank you!!

Elias Omar 1G
Posts: 52
Joined: Fri Sep 28, 2018 12:17 am

Re: Reversible vs. Irreversible

Postby Elias Omar 1G » Sun Feb 10, 2019 10:51 pm

You get more work done in a process that releases heat slowly, since less heat is lost to the surroundings. Reversible processes are infinitely slow, and therefore do the maximum amount of work.

Emily Kennedy 4L
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Re: Reversible vs. Irreversible

Postby Emily Kennedy 4L » Sun Feb 10, 2019 10:54 pm

W(reversible) will always be higher than irreversible because work is being done by the system, whereas with W(irreversible) work is being done on the system thus it is losing heat.

Steven Garcia 1H
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Joined: Fri Sep 28, 2018 12:16 am

Re: Reversible vs. Irreversible

Postby Steven Garcia 1H » Sun Feb 10, 2019 10:57 pm

Hi!

I believe it has to do with the fact that the system of a reversible process is continually adjusting in response to the external pressure. If the external pressure increases or decreases even a very small amount it will cause the piston to move in or out respectively at the expense of work. Whereas with an irreversible reaction, a change so small wouldn't affect the system and no work would be required.

Nathaniel 2E
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Joined: Mon Jun 25, 2018 3:00 am

Re: Reversible vs. Irreversible

Postby Nathaniel 2E » Sun Feb 10, 2019 10:59 pm

Think about them in terms of the "area under the curve" in a graph of Pressure x Volume. Because the reversible reaction depends logarithmically on volume, while the irreversible reaction depends linearly on volume. Therefore, the area under the curve (work) is larger for reversible, as the graph for reversible appears as a negatively sloping line, as opposed to the straight line for irreversible
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kateminden
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Re: Reversible vs. Irreversible

Postby kateminden » Mon Feb 11, 2019 2:25 pm

Nathaniel 2E wrote:Think about them in terms of the "area under the curve" in a graph of Pressure x Volume. Because the reversible reaction depends logarithmically on volume, while the irreversible reaction depends linearly on volume. Therefore, the area under the curve (work) is larger for reversible, as the graph for reversible appears as a negatively sloping line, as opposed to the straight line for irreversible


These images are really helpful! One thing I still am having trouble understanding, though, is why the external pressure is decreasing even though the volume is increasing in reversible reactions.

Brandon_Tran_2E
Posts: 63
Joined: Fri Sep 28, 2018 12:23 am

Re: Reversible vs. Irreversible

Postby Brandon_Tran_2E » Mon Feb 11, 2019 2:30 pm

Remember that PV=nRT or P1V1=P2V2, that is, pressure and volume are inversely related so an increase in volume for example leads to a decrease in pressure.


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