Question

A sample of ideal gas is placed inside a balloon at room temperature. The balloon is then put inside a freezer, where it deflates without losing any of the gas inside it. The system is the gas inside the balloon.

I - Represent this process with a PV diagram.

II - Was the change in internal energy of the system, positive, negative, or zero? How do you know?

III - Was the work done by the atmosphere on the system positive, negative, or zero? How do you know?

IV - Was the energy supplied to the system by heating positive, negative, or zero? How do you know?

V - Represent this process with a work-energy bar chart.

Answer 1

1) The given process is a constant pressure process if we consider the balloon's stiffness is zero.

Pressure of the gas inside the balloon and the pressure acting on the balloon due outside atmospheric air is same .

If there is any slight difference in pressure volume of the balloon will increase or decrease.Volume of the balloon adjusts itself such that the pressure is same both inside and outside the balloon.

If pressure inside the balloon increases volume of the balloon increase and if pressure inside the balloon decreases volume of the balloon decreases.

2) Change in internal energy dU = mCv(T2-T1)

Since it is a cooling process final temperature will be lower than initial temperature,therefore from the above realtion internal energy of the gas decreases,

Change in internal energy will be negative.

3) Here as the gas inside the balloon gets cooled its pressure & volume decreases , this is because the atmospheric gas is at higher pressure and gas inside the balloon is at lower pressure.Atmospheric gas compresses the gas inside the balloon at costant pressure.

Work done by the atmosphere on the system will be positive.

4) It is cooling process , Energy supplied will be negative.

5)

work is done on the system.

Energy of the system decrease.