Moderate

During the adiabatic expansion of 2 moles of a gas, the internal energy of the gas is found to decrease by 2 joules. The work done during the process on the gas will be equal to:

Correct answer: A. 2 J

  • A. 2 J
  • B. 1 J
  • C. -2 J
  • D. -1 J

Explanation

In an adiabatic process, there is no heat exchange with the surroundings (Q = 0). According to the first law of thermodynamics, Q = ΔU + W, where ΔU is the change in internal energy and W is the work done. For this process, ΔU = -2 J, meaning the internal energy of the gas decreases by 2 J. Substituting into the equation gives 0 = -2 J + W. Solving for W, we find that W = 2 J. This means that 2 J of work is done by the gas during the adiabatic expansion.Options B (-1 J) and D (-2 J) are incorrect as they do not satisfy the energy balance described by the first law of thermodynamics for this scenario.

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About First Law of Thermodynamics

The first law relates heat supplied, work done and the change in internal energy through energy conservation. Problems use sign conventions and apply the law to isothermal, adiabatic, isobaric and isochoric processes. Internal energy is a state function, while heat and work depend on the path followed.

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