n = 0.081 kmol of He gas initially at 27ºC and pressure = 2…

Physics Thermodynamics Mix MCQ (Single Correct)

n = 0.081 kmol of He gas initially at 27ºC and pressure = 2 × 10 5 N/m 2 is taken over the path A → B → C. For He

C v = 3R/2, C p = 5R/2.

Assume the ideal gas law.

How much work does the gas do in expanding at constant pressure from A → B?

What is the change in thermal or internal energy of the helium from A → B?

How much heat is absorbed in going from A → B?

Text Solution

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The correct answer is:

CHECK THE SOLUTION.

Sol. For A → B, the external work is

W = p A (V B – V A ) = 1.0 × 10 5 J.

For A → B, the increase of the internal energy is

Δ U = nC v Δ T = C v p A (V B – V A )/R = 3W/2 = 1.5 × 10 5 J.

By the first law of thermodynamics, the heat absorbed during A → B is W + Δ U = 2.5 × 10 5 J.

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