Question

Two cylinders A and B of equal capacity are connected to each other via a stopcock. A contains a gas at standard temperature and pressure. B is completely evacuated. The entire system is thermally insulated and the stopcock is suddenly opened. Answer the following: What is the change in internal energy of the gas?

Answer 1

The above process is known as free. expansion. in case of free expansion, no work is done by the system or on the system by the surrounding. also system is already insulated so no heat transfer has taken place to or from the system.
but we know, internal energy will be change either work should be done by the gas or on the gas. or heat should be transferred to or from the gas. but here nothing is happened so internal energy would remain same or constant or change in internal energy of gas is 0, i.e. ΔU = 0