Find the change of internal energy of the air.

[MaiteB]

Homework Statement

A car rubber has the volume 50 liters when it is bloated in a pressur 1.8 atm and in a temperature 293 K. After some hours of journey as an effect of friction the pressure will become 2atm. Find the change of internal energy of the air inside the rubber (U)

Homework Equations

U=3/2nRT

The Attempt at a Solution

I thought to sue the formula U=3/2nRT, but I don't know the n.

 

[TSny]

Don't forget the ideal gas law. Also, in the formula for U, are you sure the fraction is 3/2? Nitrogen and oxygen are diatomic gases.

 

[MaiteB]

Don't forget the ideal gas law. Also, in the formula for U, are you sure the fraction is 3/2? Nitrogen and oxygen are diatomic gases.

Ok but how can I find the U with this compound of gases like air?

 

[MaiteB]

Don't forget the ideal gas law. Also, in the formula for U, are you sure the fraction is 3/2? Nitrogen and oxygen are diatomic gases.

I am writing my solution: pV=nRT=>n=(1.8*10^5*0.05)/(8.31*293)=3.7
1.8/293=2/x=>x=325.5555
U= 5/2* 3.7*8.31*(325.56-293)=2500, but in my book the answer is 2537J

 

[TSny]

Looks good. Some of the data in the problem is given to only 2 significant figures. So, the textbook should have rounded the answer to 2 significant figures which agrees with yours.

 

[theodoros.mihos]

If you use 1.01325 x 10⁵ for atm you find a better number. Your calculation is correct.