# Find the change of internal energy of the air.

• MaiteB
In summary, the conversation discusses finding the change in internal energy of air inside a car rubber that has been bloated to 50 liters at 1.8 atm and 293 K and then experiences a pressure change to 2 atm due to friction. The solution involves using the ideal gas law and the formula for internal energy (U=3/2nRT) to calculate the change in temperature and ultimately the change in internal energy. The final answer of 2500J is rounded to 2 significant figures in the book.
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)

U=3/2nRT

## The Attempt at a Solution

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

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.

TSny said:
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?

TSny said:
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

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.

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

MaiteB

## 1. What is internal energy of air?

Internal energy of air is the total energy present in a given volume of air due to the random motion and interactions of its molecules. It includes both the kinetic and potential energies of the molecules.

## 2. How is the change in internal energy of air calculated?

The change in internal energy of air can be calculated by subtracting the initial internal energy from the final internal energy. This can be determined by considering the changes in temperature, pressure, and volume of the air.

## 3. What factors affect the internal energy of air?

The internal energy of air is affected by changes in temperature, pressure, and volume. It can also be influenced by the composition of the air, such as the presence of water vapor or other gases.

## 4. Why is it important to know the change in internal energy of air?

Knowing the change in internal energy of air is important because it allows us to understand and predict how the air will behave in different conditions. It is also crucial in various fields such as meteorology, engineering, and thermodynamics.

## 5. How can the change in internal energy of air be measured?

The change in internal energy of air can be measured using various instruments such as thermometers, pressure gauges, and volume sensors. These instruments can provide data on the changes in temperature, pressure, and volume, which can then be used to calculate the change in internal energy.

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