The internal energy of the system decreases in an adiabatic process. Which of the following must be true regarding this process?
Correct answer: B. Work is done by the system
- A. Heat flows out of the system
- B. Work is done by the system
- C. Work is done by the surroundings
- D. The potential energy of the system is changing
Explanation
According to the first law of thermodynamics, Q = ΔU + W, where Q is the heat added to the system, ΔU is the change in internal energy, and W is the work done by the system. In an adiabatic process, Q = 0, so the equation simplifies to ΔU = -W. This means that if the internal energy decreases, W must be positive, indicating that work is done by the system on the surroundings. Thus, the correct answer is that work is done by the system. The other options are incorrect because they either suggest heat transfer (which does not occur in an adiabatic process) or involve potential energy, which is not directly related to the described process.
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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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