A system absorbs 10 kJ of heat at a constant volume and its temperature rises from 270 °C to 370 °C. The value of ∆U is:
Correct answer: B. 10 kJ
- A. 100 kJ
- B. 10 kJ
- C. 0 kJ
- D. 1 kJ
Explanation
The correct answer is 10 kJ because, according to the first law of thermodynamics, the change in internal energy (∆U) is equal to the heat absorbed minus the work done by the system. At constant volume, no work is done, so all the heat absorbed (10 kJ) results in an increase in internal energy. Option A (100 kJ) and Option D (1 kJ) both inaccurately represent the energy change, while Option C (0 kJ) incorrectly suggests no change in internal energy despite heat being absorbed.
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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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