Question

For an ideal gas undergoing isothermal irreversible expansion:
(A) $\Delta U=0$
(B) $\Delta H=0$
(C) $\Delta S=0$
(D) $\Psi =0$

Answer 1

Hint: In thermodynamics, the system consists of those molecules which are reacting with collection of objects and rest of the system in the universe is surroundings. System in thermodynamics is three types, closed, open and isolated systems.

Complete answer:
A process or change is said to be reversible, if a change is brought out in such a way that the process could be reversed by an infinitesimal change. A reversible process proceeds infinitely slowly by a series of equilibrium states such that the system and the surroundings are always in near equilibrium with each other.
Processes other than reversible processes are known as irreversible processes.
Isothermal expansion of an ideal gas is an expansion of gas at constant temperature of the system , at change of heat with system and surroundings throughout the process.
In an isothermal process, $\Delta T=0$ then $\Delta U=0$ , hence there is no change in the internal energy at constant temperature.
Since, \[\begin{align}
  & \Delta U=n{{c}_{p}}\Delta T=0 \\
 & \Delta H=n{{c}_{p}}\Delta T=0, \\
\end{align}\]
 Free expansion of a gas occurs when it is subjected to expansion in an irreversible process.
Hence, for an ideal gas isothermal irreversible expansion, $\Delta U=0\And \Delta H=0$

The correct answer is option A and B.

Note:
The reversible isothermal expansion of an ideal gas is a spontaneous process, because at equilibrium the density of gas is uniform throughout the system. If the process is at infinitely slowly so that microscopic reverse from the final state exactly generates the initial state at constant temperature with increase in the volume.