A fixed mass of gas in a thermally insulated container is compressed. After compression, the temperature of the gas will have:
Correct answer: D. Risen, since doing work on the gas increases the kinetic energy of the molecules
- A. Fallen, since more molecules bombarded the container and so they must be moving slower
- B. Fallen, since more molecules collide more frequently with one another and so their average speed is lower
- C. Remains constant if the compression is very slow
- D. Risen, since doing work on the gas increases the kinetic energy of the molecules
- E. Risen, since there are more intermolecular collisions and so more heat is produced by them
Explanation
If an ideal gas is compressed adiabatically, its temperature rises because the heat produced cannot be lost to the surroundings. Each molecule has more KE than before because of collisions of molecules with moving parts of the wall (i.e., piston compressing the gas).
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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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