What happens if you put a plastic bag over jar of water?

When a plastic bag is placed over a jar of water, the air inside the bag will create an airtight seal, preventing air from entering or escaping. As the temperature increases, the air inside the bag will expand, causing the bag to inflate like a balloon. This phenomenon is a result of the Charles' Law, which states that the volume of a gas is directly proportional to its temperature, when the pressure remains constant. As the temperature increases, the molecules of the gas move more rapidly and collide with the bag more frequently, causing it to expand.