## Homework 8.49

$\Delta U=q+w$

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Sonia Perez 1G
Posts: 29
Joined: Fri Sep 25, 2015 3:00 am

### Homework 8.49

The homework problem reads:
Oxygen difluoride is a colorless, very poisonous gas that reacts rapidly with water vapor to produce O2, HF, and heat:

OF2 + H2O--> O2 + 2HF delta H= -318 kj
What is the change in internal energy for the reaction of 1.00 mol OF2?

I do not understand why the formula PV=nRT is used to solve this problem, when no volume or pressure are indicated.

WhitneyLaValle4A
Posts: 23
Joined: Fri Sep 25, 2015 3:00 am

### Re: Homework 8.49

If no pressure or volume are indicated then it is used to find the number of moles or temperature as R is given

Diego Zavala 2I
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### Re: Homework 8.49

$\Delta U=q+w$ and $w=-P \Delta V$ . Since we are not given volume or external pressure, we substitute -PV for nRT (PV=nRT).

Hence, we get the equation $\Delta U= q -nRT$

$q=\Delta H=-318kJ$
R=3.145
T=298K
$\Delta n$ = (3 moles of gas in products)-(2 moles of gas in reactants)= 1

April P 1C
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### Re: Homework 8.49

How did you get T=298?

miznaakbar
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### Re: Homework 8.49

Since the question doesn't specify, we can assume it is at room temperature (which is 298K).

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