NEETChemistryThermodynamics (C)
Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): When an ideal gas undergoes isothermal expansion into a vacuum, the heat absorbed is zero. Reason (R): In an isothermal expansion of an ideal gas, the change in internal energy is zero and the work done against a vacuum is zero. In the light of the above statements, choose the most appropriate answ
Options
- ABoth (A) and (R) are true and (R) is the correct explanation of (A)
- BBoth (A) and (R) are true but (R) is not the correct explanation of (A)
- C(A) is true but (R) is false
- D(A) is false but (R) is true
Correct answer
A. Both (A) and (R) are true and (R) is the correct explanation of (A)
Step-by-step solution
For an isothermal expansion of an ideal gas, the temperature remains constant ( T = 0 ). Since the internal energy of an ideal gas depends only on temperature, the change in internal energy is zero ( U = 0 ). Expansion into a vacuum means the external pressure is zero ( P_ ext = 0 ). Thus, the work done is zero ( W = -P_ ext V = 0 ). According to the first law of thermodynamics, U = q + W . Substituting the values gives 0 = q + 0 , which means the heat absorbed ( q ) is zero. Therefore, both Assertion (A) and Reaso