# Homework Help: Thermodynamics & Thermal Energy

1. Dec 9, 2007

### dals2002

(SOLVED)Thermodynamics & Thermal Energy

1. The problem statement, all variables and given/known data
a 6.0m X 8m X 3m room contains air at 20 Degrees Celcius

2. Relevant equations
What is the room's thermal energy

3. The attempt at a solution

now i know that oxygen is a diatomic atom so i used

E(thermal)= 5/2 NkbT= 5/2 nRT

i tried to find the amount of moles by doing pv=nrt -> 5/2 pv=5/2 nRT but i don't know either the pressure exerted neither the number of moles

so i was think to find pV i could use pV= 2/3N*$$(\epsilon)$$(Average Translational kinetic energy)
where $$(\epsilon)$$= 3/2 KbT

so i have one question would it work like that?

Last edited: Dec 9, 2007
2. Dec 9, 2007

### dals2002

any info or help is appreciated, anything cause i have no idea if that process is right

3. Dec 9, 2007

### Roger Wilco

I am not sure, but I believe you could find n by using the volume of the room and the fact that it is at 20 Celsius.

That is since density=mass/volume.

I am just guessing though.

RW

4. Dec 9, 2007

### Andrew Mason

Use n = PV/RT to find the number of moles. Then use:

$$U = \frac{5}{2}nRT$$ where T = temperature in Kelvins, to find the total internal energy of the air.

This, of course, assumes it is a perfect ideal gas so that the heat capacity of the air is 5R/2 at all temperatures which is not true.

AM

Last edited: Dec 9, 2007
5. Dec 9, 2007

### dals2002

yeah i took a look at that but because the temperature is higher than STP i don't know density or mass

6. Dec 9, 2007

### Andrew Mason

You are supposed to assume that it is at atmospheric pressure. It is a room in a building, not a sealed chamber.

AM

7. Dec 9, 2007

### dals2002

WOW thanks this really helped me i didn't knew that the temperature didn't affect the atmospheric pressure, i solved it thanks