Express the change in internal energy of a system when
(i) No heat is absorbed by the system from the surroundings, but work (w) is done on the system. What type of wall does the system have ?
ii) No work is done on the system, but q amount of heat is taken out from the system and given to the surroundings. What type of wall does the system have?
(iii) w amount of work is done by the system and q amount of heat is supplied to the system. What type of system would it be?

Explanation

(i) `Delta U=w_(ad)` Wall is adiabatic
(ii) `Delta U=-q` thermally conducting walls
(iii) `Delta U=q-w,` closed system.