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COMEDK2021ChemistryThermodynamics (C)

When the expansion of a gas occurs in vaccum and at constant volume, then

Options

  1. AU=q V
  2. BU=q p
  3. CH=q V
  4. DH=q p

Correct answer

A. U=q V

Step-by-step solution

For any thermodynamic process, the first law of thermodynamics is given by U = q + w , where w is the work done on the system. In the case of expansion in a vacuum, the external pressure P_ ext = 0 . Since w = - P_ ext dV , the work done w = 0 . At constant volume, the change in volume dV = 0 , which also implies w = 0 . Substituting w = 0 into the first law equation, we get U = q . Since the process occurs at constant volume, the heat exchanged is denoted as q_V . Therefore, U = q_V . Answer: U=q V

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