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Reversible vs. Irreversible

Posted: Sun Feb 10, 2019 10:38 pm
by 905085650
Can someone explain to me why W(reversible) is greater than W(irreversible)? Thank you!!

Re: Reversible vs. Irreversible

Posted: Sun Feb 10, 2019 10:51 pm
by Elias Omar 1G
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.

Re: Reversible vs. Irreversible

Posted: Sun Feb 10, 2019 10:54 pm
by Emily Kennedy 4L
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.

Re: Reversible vs. Irreversible

Posted: Sun Feb 10, 2019 10:57 pm
by Steven Garcia 1H
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.

Re: Reversible vs. Irreversible

Posted: Sun Feb 10, 2019 10:59 pm
by Nathaniel 2E
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

Re: Reversible vs. Irreversible

Posted: Mon Feb 11, 2019 2:25 pm
by kateminden
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.

Re: Reversible vs. Irreversible

Posted: Mon Feb 11, 2019 2:30 pm
by Brandon_Tran_2E
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.