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

u200bu200bu200bu200bu200bu200bu200b

From the process equation and ideal gas law

PV = mRT = constant

we can calculate the work term

consistent with the above result.