Question

Consider a small air ** with a cylinder volume of 1 cm3 at 250 kPa, 27°C. The bullet acts as a piston initially held by a trigger. The bullet is released so the air expands in an adiabatic process. If the pressure should be 100 kPa as the bullet leaves the cylinder find the final volume and the work done by the air.

Answer 1

C.V. Air. Assume a reversible, adiabatic process.

Energy Eq. u2 - u1 = 0 − 1w2 ;

Entropy Eq s2 - s1 = ∫ dq/T + 1s2 gen = 0

State 1: (T1,P1) State 2: (P2, ?

So we realize that one piece of information is needed to get state 2.

Process: Adiabatic 1q2 = 0 Reversible 1s2 gen = 0

With these two terms zero we have a zero for the entropy change. So this is a constant * (isentropic) expansion process giving s2 = s1.