Answer to Question #115983 in Molecular Physics | Thermodynamics for Oluchi

Question

In an air motor cylinder the compressed air has an internal energyof 450kg/kj at the beginning of the expansion and an internal energy of 220kg/kj after expansion. If the work done by air during the expansion is 120kg/kj,calculate the heat flow to and fro the cylinder and state if the system gain or losses heat

Answer 1

As per the question,

Internal energy of the compressed air $(U_1)=450kg/KJ$

Internal energy after expansion$(U_2)=220 kg/kJ$

Work done by air during expansion$(W)=120 kg/KJ$

$Q=W+(U_2-U_1)$

$Q=120+(220-450)=120-230=-110kg/KJ$

Here negative sign is showing that heat rejected by the air is 110 kg/KJ, so here heat is getting loss.