If a system absorbs 2090 J of heat and does 400 J of work, then the change in internal energy of the system will be
Correct answer: C. 1690 J
- A. -1690 J
- B. 0 J
- C. 1690 J
- D. 2490 J
Explanation
The First Law of Thermodynamics states that the change in internal energy (ΔU) of a system is equal to the heat added to the system (Q) minus the work done by the system (W). In this problem, the system absorbs 2090 J of heat and does 400 J of work. Therefore, the change in internal energy is calculated as ΔU = Q - W = 2090 J - 400 J = 1690 J. Option A (-1690 J) is incorrect because it miscalculates the direction of energy change. Option B (0 J) is incorrect because it assumes no net change in energy, which contradicts the given values. Option D (2490 J) incorrectly adds the work instead of subtracting it, leading to an erroneous calculation.
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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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