## 4D.7

805312064
Posts: 50
Joined: Thu Jul 11, 2019 12:16 am

### 4D.7

Oxygen difluoride is a colorless, very poisonous gas that reacts rapidly and exothermically with water vapor to produce O2 and HF:
OF2(g) + H2O(g) -> O2(g) + 2 HF(g) deltaH = -318 kJ
What is the change in internal energy for the reaction of 1.00 mol OF2?

I understand that we have to find q, and to use -delta nRT, but how do you know what the temperature is? The answer key uses 298 Kelvin, but where did that come from?

Jacey Yang 1F
Posts: 101
Joined: Fri Aug 09, 2019 12:17 am

### Re: 4D.7

298K is the most common temperature used in data for reaction enthalpies, so we just have to assume that when no temperature is stated.

805312064
Posts: 50
Joined: Thu Jul 11, 2019 12:16 am

### Re: 4D.7

Thank you! Is this always going to be the case if there is no given temperature?

Ruby Richter 2L
Posts: 103
Joined: Thu Jul 25, 2019 12:17 am

### Re: 4D.7

When do you need to change the temperature from celsius to kelvin and when is it okay to leave T as celsius in an equation?

805312064
Posts: 50
Joined: Thu Jul 11, 2019 12:16 am

### Re: 4D.7

I think if it's ever the difference in T (delta T), then there's no need to convert. However, if you're using T to calculate something else, like in the ideal gas equation, then you need to convert to Kelvin!

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