Dear all, I would like to ask: Given a control volume (V1), at an initial temperature (T1), the pressure (P1) in the volume (V1) is decreased by sucking out air. The suction hole is then closed to achieve a state of P2 * V2 = n2 * R * T2 . What would happen to the temperature in the control volume? (ie would T2 > T1 or T2 < T1) From my understanding: " By sucking out air it means reducing the number of moles (n) of air from the control volume. P1 * V1 = n1 * R * T1 P2 * V2 = n2 * R * T2 so given that R is constant, T2 = ( P2 / P1 ) * ( n1 / n2 ) * T1 so if ( P2 / P1 ) * ( n1 / n2 ) < 1, then T2 < T1, and otherwise is true. " Is my understanding correct? and if yes, how do i determine whether ( P2 / P1 ) * ( n1 / n2 ) > 1 or ( P2 / P1 ) * ( n1 / n2 ) < 1 ? Thanks and best regards, Andrew.