## Finding change in internal energy using PV=nRT equation

Rachael_1H
Posts: 31
Joined: Fri Sep 25, 2015 3:00 am

### Finding change in internal energy using PV=nRT equation

Hi, I'm looking for help with homework question 8.49, which states,

"Oxygen difluoride is a colorless, very poisonous gas that reacts rapidly with water vapor to produce O2, HF, and heat.

It gives the formula

OF2 (g) +H20 (g) --> O2 (g) + 2HF (g) with delta H being -318 kJ.

What is the change in internal energy for the reaction of
1.00 mol OF2?"

I understand that we use the equation PV=nRT to find PV and then find change in internal energy for the rxn by using the equation:
(delta U)=(delta H)-(PV)

I am just confused about what value we use for T when solving for PV using the equation PV=nRT? The answer key has the equation as PV=(1 mole)(gas constant)(298 K)=2.48 kJ. Where did the answer key derive the value T=(298 K) from?

Thanks!

204643643
Posts: 10
Joined: Wed Nov 18, 2015 3:00 am

### Re: Finding change in internal energy using PV=nRT equation

298 Kelvin is the same as 25 Celsius, the standard temperature that is typically used in various equations and formulas. Hope this helped.

Austin Vo 1K
Posts: 28
Joined: Fri Sep 25, 2015 3:00 am

### Re: Finding change in internal energy using PV=nRT equation

I'm guessing that they may have left out the information for the temperature at which the reaction took place in the textbook. Usually, the temperature would be given in the problem.

Leonardo Le Merle 1D
Posts: 56
Joined: Wed Feb 27, 2019 12:16 am

### Re: Finding change in internal energy using PV=nRT equation

Since the reaction doesn't specify, we can assume T=298K (room temperature). However, this is a typo on the textbook's part; they should have specified T.

Return to “Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)”

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