## HW 4D7

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

### HW 4D7

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

Eugene Chung 3F
Posts: 142
Joined: Wed Nov 15, 2017 3:03 am

### Re: HW 4D7

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.

Posts: 111
Joined: Thu Jul 25, 2019 12:17 am

### Re: HW 4D7

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

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?

Posts: 116
Joined: Thu Jul 25, 2019 12:15 am

### Re: HW 4D7

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?