Explain internal energy as a state function.

Explanation

Internal energy depends only on the state variables P, V, T and n. When the system is changed from the initial state to the final state, the change in interal energy is same for the different paths taken.
(a) In a cyclic process, the net change in U is zero.
(b) In an isothermal process, the change in U of an ideal gas is zero.
(c ) In an adiabatic process, U of a system decreases if work done by the system.
(d) If heat is absorbed by the system, its U increases.
(e) If heat is released from the system, its U decreases.