Find the change in internal energy of the system when a system absorbs 2 kilocalorie of heat and at the same time does 500 joules of work.
Correct answer: C. 7900J
- A. 8200J
- B. 5600J
- C. 7900J
- D. 6400J
Explanation
The change in internal energy (∆U) of a system can be found using the First Law of Thermodynamics: ∆U = ∆Q - ∆W, where ∆Q is the heat absorbed by the system and ∆W is the work done by the system.In this problem, the system absorbs 2 kilocalories of heat, which needs to be converted to joules: 2 kcal = 2 x 1000 x 4.2 J = 8400 J. The work done by the system is 500 J.Therefore, ∆U = 8400 J - 500 J = 7900 J, which is correctly represented by Option C.Other options are incorrect due to mistakes in unit conversion or incorrect application of the formula.
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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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