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MHT CET202618 April 2026Morning ShiftChemistryThermodynamics (C)Actual

Which from following is correct expression of first law of thermodynamics for isothermal process?

Options

  1. AW = - Q
  2. B- U = - W
  3. CU = Q _ v
  4. DQ _ p = U + P _ ext V

Correct answer

A. W = - Q

Step-by-step solution

According to the first law of thermodynamics, the change in internal energy is given by U = Q + W . For an isothermal process, the temperature of the system remains constant, so T = 0 . Since the internal energy of an ideal gas depends only on temperature, the change in internal energy is zero, U = 0 . Substituting U = 0 into the first law equation gives: 0 = Q + W W = -Q Answer: W = - Q

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