## 8.49

Megan Purl 1E
Posts: 49
Joined: Fri Sep 29, 2017 7:07 am

### 8.49

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

I understand the process of how to solve for this equation but in the solutions manual it solves using PV=nRT and it plugs in T as 298K. I was just wondering how that number was calculated because it doesn't state the temperature in the problem.

Shane Simon 2K
Posts: 30
Joined: Fri Sep 29, 2017 7:05 am

### Re: 8.49

Whenever no temperature is given but a temperature is needed to solve, you assume the temperature is 25.0 degrees Celcius which is 298 K.

Oscar Valdovinos 1I
Posts: 29
Joined: Fri Sep 29, 2017 7:05 am

### Re: 8.49

I think you assume ideal gases, which is why we use Pv=nRT. Also in ideal gases tempature is always 25 degrees celsius or 298 kelvin

Helen Shi 1J
Posts: 78
Joined: Sat Jul 22, 2017 3:00 am

### Re: 8.49

Since using Kelvin or Celcius will give different answers, which one should we use?

Varsha Swamy 2J
Posts: 14
Joined: Sat Jul 22, 2017 3:00 am

### Re: 8.49

I think we should use Kelvin in problems where it makes a difference because that is the SI unit for temperature.
For problems where the equation just asks for a change in temperature, using Kelvin or Celsius will yield the same result.

Matthew Lin 2C
Posts: 30
Joined: Fri Sep 29, 2017 7:06 am

### Re: 8.49

Helen Shi 1J wrote:Since using Kelvin or Celcius will give different answers, which one should we use?

I would definitely use Kelvin, but if you're only calculating the change in temperature, you can use either Kelvin or Celsius.