Confusion about entropy formula


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OliviaShearin2E
Posts: 37
Joined: Fri Sep 29, 2017 7:05 am

Confusion about entropy formula

Postby OliviaShearin2E » Mon Jan 22, 2018 10:11 pm

apparently only works for heat transferred reversibly. How do we know when the situation has heat transferred reversibly, and what exactly does this mean? Quite a few of the homeworks so far have used this equation but there is no specification on the method of heat transfer. I am really confused because chapter 8 was really explicit about a system expanding reversibly or at constant pressure.

OliviaShearin2E
Posts: 37
Joined: Fri Sep 29, 2017 7:05 am

Re: Confusion about entropy formula

Postby OliviaShearin2E » Mon Jan 22, 2018 10:11 pm

Does this basically mean the reaction takes place at a constant temperature?

Remi Lathrop 1G
Posts: 51
Joined: Fri Sep 29, 2017 7:07 am

Re: Confusion about entropy formula

Postby Remi Lathrop 1G » Thu Jan 25, 2018 11:55 am

I am also confused about reversible reactions, but I believe it may mean a reaction that can occur forwards and backwards without an increase in entropy.

Laura Riccardelli
Posts: 49
Joined: Fri Sep 29, 2017 7:04 am

Re: Confusion about entropy formula

Postby Laura Riccardelli » Thu Jan 25, 2018 12:01 pm

I think that the reversible problems occur in heat reservoir so they have a constant temperature all the time.

Sally Nason - 1K
Posts: 40
Joined: Fri Sep 29, 2017 7:05 am

Re: Confusion about entropy formula

Postby Sally Nason - 1K » Thu Jan 25, 2018 12:04 pm

If there is a heat reservoir in the surroundings, the temperature will be constant and therefore heat will be reversible. If a system is doing work, it is losing energy but heat from the surroundings can be added to the system to replace the energy lost. For instance, during a phase change, work is being done by the system to change the phase of a substance, such as from ice to liquid water. The temperature of the system does not change, yet the enthalpy does. Therefore, heat (q) must be going into the system. You should also be aware that deltaS = q/T is equivalent to nRTln(V2/V1).

Laura Riccardelli
Posts: 49
Joined: Fri Sep 29, 2017 7:04 am

Re: Confusion about entropy formula

Postby Laura Riccardelli » Thu Jan 25, 2018 12:20 pm

Also,most biological systems are irreversible because that needs less work then reversible expansion.

Katie Lam 1B
Posts: 52
Joined: Fri Sep 29, 2017 7:06 am

Re: Confusion about entropy formula

Postby Katie Lam 1B » Thu Jan 25, 2018 2:45 pm

Reversible reactions occur when a system is in thermodynamic equilibrium with its surroundings, while this is not true for irreversible reactions.


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