## Homework 8.49 question

Shreya Narain 2J
Posts: 22
Joined: Fri Sep 25, 2015 3:00 am

### Homework 8.49 question

Oxygen difluoride is a colorless, very poisonous gas that reacts rapidly with water vapor to produce O2, HF, and heat: What is the change in internal energy for the reaction of 1.00 mol OF2. $\Delta H = -318kJ$

For this question, I know that $\Delta U = q + w$ and the heat released is 318kJ, how exactly do I find the work? I also know that $w = -P\Delta V$ but what exactly do with that?

KVu 3G
Posts: 12
Joined: Fri Sep 25, 2015 3:00 am

### Re: Homework 8.49 question

You find w using w=-P * delta V which can be derived from the ideal gas equation.

PV=nRT
$P\Delta V = \Delta n RT$
$-P\Delta V =- \Delta n RT$

Substitute $-P\Delta V$ for $- \Delta n RT$ gives you $w=-\Delta nRT$.

New equation is $\Delta U=q + (-\Delta nRT)$ where q is given, R is a constant, T=298K, and $\Delta n$=1 mol

Aaron Knuteson 3K
Posts: 9
Joined: Fri Sep 25, 2015 3:00 am

### Re: Homework 8.49 question

This may be a dumb question, but where is the 298K coming from?

Thanks!

Joshua Kim 3H
Posts: 21
Joined: Fri Sep 25, 2015 3:00 am

### Re: Homework 8.49 question

I believe the 298K comes from assuming that the temperature was at the standard state of usually 25 deg. Celsius making 273+25=298K

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