A container is divided into two equal portions. One portion contains an ideal gas at pressure P and temperature T while the other portion is a perfect vacuum. If a hole is opened between two portions:
Correct answer: C. There will be no change in internal energy.
- A. There will be a change in internal energy.
- B. There will be a change in temperature.
- C. There will be no change in internal energy.
- D. The external pressure will increase
- E. The external pressure will decrease.
Explanation
When the gas expands through a hole, it is free expansion, therefore the pressure is 0 and thus according to W=PV, the work done also is 0.Since the container is insulated so the change in heat energy is also 0, hence according to the equation:Q=U+WThe change in internal energy is also 0.Also, since internal energy is directly proportional to temperature of the gas hence, there will be no change in temperature as well.
This question appeared on the NUMS 2017 paper, which you can sit online with every answer explained.
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About First Law of Thermodynamics
The first law relates heat supplied, work done and the change in internal energy through energy conservation. Problems use sign conventions and apply the law to isothermal, adiabatic, isobaric and isochoric processes. Internal energy is a state function, while heat and work depend on the path followed.
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