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MHT CET202618 April 2026Evening ShiftChemistryThermodynamics (C)Actual

Which of the following is the correct expression of the first law of thermodynamics for adiabatic processes ?

Options

  1. AW = -Q
  2. B- U = -W
  3. CU = QV
  4. DU = Q_P - P_ ext , V

Correct answer

B. - U = -W

Step-by-step solution

According to the first law of thermodynamics, the change in internal energy is given by U = Q + W . For an adiabatic process, there is no heat exchange between the system and the surroundings, which means Q = 0 . Substituting Q = 0 into the first law equation, we get U = W . Multiplying both sides by -1 , this can be written as - U = -W . Answer: - U = -W

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