If heat energy of 100 J is taken out but 400 J work is done on the system, the change in internal energy is:
Correct answer: B. 300 J
- A. -300 J
- B. 300 J
- C. -100 J
- D. 0 J
Explanation
ΔQ=ΔW+ΔU100 J =400 J+ΔU100 J - 400 J= ΔUΔU=300 J
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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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