Question

A mass of 1 kg of air contained in a cylinder at 1.5 MPa, 1000 K, expands in a reversible isothermal process to a volume 10 times larger. Calculate the heat transfer during the process and the change of entropy of the air.

Answer 1

C.V. Air, control mass.

Energy Eq.  m(u₂ - u₁) = ₁Q₂ - ₁W₂ = 0

Process: T = constant so with ideal gas => u₂ = u₁ 

C.V. Air, control mass.

Energy Eq.  m(u₂ - u₁) = ₁Q₂ - ₁W₂ = 0

Process: T = constant so with ideal gas => u₂ = u₁ 

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From the process equation and ideal gas law

PV = mRT = constant

we can calculate the work term

consistent with the above result.