HW 4D7

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205154661_Dis2J
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HW 4D7

Postby 205154661_Dis2J » Sun Feb 09, 2020 11:45 pm

For 4D7, why are we using the equation DeltaH= DeltaU + DeltaNRT? I do not quite understand why we are including DeltaNRT.

Eugene Chung 3F
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Re: HW 4D7

Postby Eugene Chung 3F » Sun Feb 09, 2020 11:48 pm

205154661_Dis2J wrote:For 4D7, why are we using the equation DeltaH= DeltaU + DeltaNRT? I do not quite understand why we are including DeltaNRT.


We know that delta U = heat + w and that in this case, delta H= heat. We also know that w=-P deltaV. The ideal gas law states PV=nRT. So, -P delta V = -delta nRT.

Prasanna Padmanabham 4I
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Re: HW 4D7

Postby Prasanna Padmanabham 4I » Sun Feb 09, 2020 11:55 pm

For gases, the change in enthalpy is defined by that equation. This is because when gas is produced work is done to clear the other gases so the enthalpy is lower than the internal energy. This is explained in detail on pg 274 in the textbook (4D.2)

205154661_Dis2J
Posts: 109
Joined: Wed Sep 18, 2019 12:21 am

Re: HW 4D7

Postby 205154661_Dis2J » Mon Feb 10, 2020 12:05 am

Prasanna Padmanabham 4I wrote:For gases, the change in enthalpy is defined by that equation. This is because when gas is produced work is done to clear the other gases so the enthalpy is lower than the internal energy. This is explained in detail on pg 274 in the textbook (4D.2)


Thank you so much for explaining! Do you know why we assume that T is 298k? Is that because we are assuming that it is at room temperature?

Daria Azizad 1K
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Joined: Thu Jul 25, 2019 12:15 am

Re: HW 4D7

Postby Daria Azizad 1K » Mon Feb 10, 2020 12:36 am

Prasanna Padmanabham 4I wrote:For gases, the change in enthalpy is defined by that equation. This is because when gas is produced work is done to clear the other gases so the enthalpy is lower than the internal energy. This is explained in detail on pg 274 in the textbook (4D.2)

Where does that formula come from? Shouldn't nRT = 0 since delta V is 0?


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