According to the first law of thermodynamics, ΔU = Q + W, where ΔU Is the increase in internal energy of the system, Q is the heat transferred to the system and W is the external work done on the system.Which of the following is NOT a correct expression?
Correct answer: B. When no work is done: ΔU = -W
- A. At constant temperature: Q = -W
- B. When no work is done: ΔU = -W
- C. Work done on the system: ΔU = Q - P Δ V
- D. When work is done by the system: ΔU = Q - W
Explanation
The equation provided in the question follows the first convention, according to which B is not correct. Option C and D are correct because in physics, work done by system is positive while work done on system is negative. The reverse is for chemistry.
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About First Law of Thermodynamics
The first law states that energy is conserved, so the change in a system's internal energy equals heat supplied plus work done on the system, ΔU = q + w. Questions use sign conventions, expansion and compression work, state functions versus path functions, and the relation between internal energy and enthalpy.
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