# Internal Energy of air

#### tom_robinson1

1. Homework Statement

2. Homework Equations

3. The Attempt at a Solution

I'm currently studying A2 physics and I'm stumped on a particular question within a past paper involving internal energy of air. The question is as follows:

Estimate the internal energy of the air in a room of volume 24m^3 at a temperature of about 20˚C. Assume that the air behaves as an ideal gas at atmospheric pressure. Here are some useful formulae and data. There are several ways to make this estimate. You do NOT need to use all of the information.

pV=nRT is the equation of state of n moles of an ideal gas
kinetic energy of n moles of an ideal gas = 3/2 nRT

data:
R = 8.31 J mol^-1 K^-1
density of air = 1.3 kg m^-3
molar mass of air = 0.030 kg mol^-1
atmospheric pressure = 1.0x10^5 Pa

Internal Energy = .......................................J

Any Ideas, Regards Tom

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#### cristo

Staff Emeritus
Well, how many moles of an ideal gas are there in a volume of 24m3?

#### tom_robinson1

i got 22.97 mols using the info provided

#### chemhelper

Just in general, do you know how many moles are in 1 liter of an ideal gas? And from there how many moles are one cubic meter?

Last edited by a moderator:

#### tom_robinson1

Just in general, do you know how many moles are in 1 liter of an ideal gas? And from there how many moles are one cubic meter?
mate a litre..(not a liter!) refers to an amount of liquid not gas and there is not a set amount of moles in a litre as the volume of gas can change with regards to pressure and temprature as shown in the equation PV/T=constant (p=pressure, V=volume, T=temprature)

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