Mechanical Engineering - Thermodynamics - Discussion

Enthalpy is a constant pressure & volume.

The free expansion process is an expanded in volume increase and pressure decrease.

So, constant enthalpy is correct.

For an ideal gas, temp remains constant during the free expansion process and internal energy & enthalpy both are a function of temperature so it becomes zero.

But this is not true for real gases.

And in question nothing mention about gases.

So, option incorrect should be the answer.

Well known that in free expansion temperature remains constant so internal energy must be constant.

But on another hand, because enthalpy is a point function and in this by considering the only initial and final point. It follows Boyle's law( PV=C). It is already seen that internal energy U is constant and so (U+PV)=C, and hence enthalpy remains constant.