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NEET CHEMISTRYEasy

The work done to contract a gas in a cylinder is 462 joules. 128 joule energy is evolved in the process. What will be the internal energy change in the process? [MP PMT 2003]

A
  • 590 joules
B

– 334 joules

C
  • 334 joules
D

– 590 joules

Step-by-Step Solution

To determine the change in internal energy (ΔU\Delta U), we apply the First Law of Thermodynamics, which is mathematically expressed as ΔU=q+w\Delta U = q + w .

  1. Work (ww): According to the IUPAC sign convention used in thermodynamics, work done on the system (such as during compression or contraction) is assigned a positive sign . Therefore, w=+462w = +462 J.
  2. Heat (qq): Heat evolved (released) by the system to the surroundings is assigned a negative sign . Therefore, q=128q = -128 J.
  3. Calculation: Substituting these values into the first law equation: ΔU=(128 J)+(+462 J)=+334 J\Delta U = (-128\text{ J}) + (+462\text{ J}) = +334\text{ J}.

The internal energy of the system increases by 334 joules, which matches Option C.

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