### reversible reactions

Posted:

**Sun Feb 09, 2020 10:49 pm**How do I know which equation to use for work without the question stating whether the reaction is reversible or irreversible? Alluding to problem 4B.5 :)

Created by Dr. Laurence Lavelle

https://lavelle.chem.ucla.edu/forum/

https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=77&t=58863

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Posted: **Sun Feb 09, 2020 10:49 pm**

How do I know which equation to use for work without the question stating whether the reaction is reversible or irreversible? Alluding to problem 4B.5 :)

Posted: **Sun Feb 09, 2020 10:51 pm**

I believe the question states it if its reversible, which is the only scenario where we'd use the reversible reaction equation for W.

Posted: **Sun Feb 09, 2020 10:53 pm**

i'm pretty sure it should always tell us reversible or irreversible to indicate which equation to use.

Posted: **Sun Feb 09, 2020 10:57 pm**

Isobaric (no change in pressure) means it is an irreversible reaction. Work is found through W=P*deltaV or W=n*R*deltaT and q can be found from q=n*Cp*deltaT.

Isothermal (no change in temperature) is reversible. DeltaU (internal energy) is equal to zero so w=-q or -w=q. Work is found from W=n*R*T*ln(V2/V1) or W=n*R*T*ln(P1/P2)

There are more equations to know for each one but these allow me to distinguish the two.

Isothermal (no change in temperature) is reversible. DeltaU (internal energy) is equal to zero so w=-q or -w=q. Work is found from W=n*R*T*ln(V2/V1) or W=n*R*T*ln(P1/P2)

There are more equations to know for each one but these allow me to distinguish the two.

Posted: **Sun Feb 09, 2020 11:02 pm**

It will be said if it is reversible.