## 4D7

Samantha Hoegl Roy 2C
Posts: 81
Joined: Fri Sep 28, 2018 12:15 am

### 4D7

OF2 + H20 -> O2 + 2HF
ΔH = - 318kJ

what is the change in internal energy for the reaction of 1.00 mol OF2?
why is -PΔV = -ΔnRT used? isnt the change is ΔU = q + w; where does -ΔnRT come from?

Phan Tran 1K
Posts: 29
Joined: Fri Sep 28, 2018 12:19 am

### Re: 4D7

-PΔV = -ΔnRT is used to calculate w, which can be calculated using the equation w=-P*ΔV. You need to calculate w in order to calculate ΔU.

I don't have the seventh edition, so is there anymore information that the book gives you? Like whether the reaction is reversible or irreversible, or whether T/P/V is constant? Because all of these things play a big part in which equation you should use to find w (or whether you need to find w at all)

Gary Qiao 1D
Posts: 66
Joined: Fri Sep 28, 2018 12:26 am

### Re: 4D7

The change in internal energy is ΔU = q + w. The problem gives you q as q = -318 kJ, so we have to find w, or the work done in by the system due to the reaction. w could be found by -PΔV, which means ΔU = q + -PΔV. Because they did not give the volume or pressure, we could convert -PΔV to -ΔnRT because of the formula PΔV = ΔnRT, in which adding a negative to PΔV would result in -ΔnRT. Ultimately, we get ΔU = q -ΔnRT to find ΔU.

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