A sealed, rigid container initially qualifies as isolated. After several hours, a slow leak develops through a tiny pinhole, allowing a small amount of gas to escape while the wall remains thermally insulating. Which statement is most accurate about the total internal energy of the gas that remains inside the container after the leak begins?
(a) It remains unchanged because the container wall still prevents heating and boundary work.
(b) It decreases because energy leaves the container along with the escaping gas molecules.
(c) It increases because the pressure drop in the fixed volume does negative work on the gas.
(d) It keeps decreasing toward zero because all of the gas’s energy will eventually escape with the molecules.