The mathematical statement of the first law of thermodynamics is
Correct answer: A. change in internal energy equals heat added plus work done on the system
- A. change in internal energy equals heat added plus work done on the system
- B. change in internal energy equals heat added minus temperature
- C. enthalpy equals internal energy divided by pressure
- D. heat equals work in every process
Explanation
The internal energy of a system can be raised either by heating it or by doing work on it, and the equation simply accounts for both routes. When the system does work on the surroundings, for example by expanding against the atmosphere, that term becomes negative. The sign conventions must be stated clearly, since they are the commonest source of error.
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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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