If a cup of water is sealed inside a plastic bag and left overnight in a warm area what will happen?

If a cup of water is sealed inside a plastic bag and left overnight in a warm area, the heat will cause some of the water to evaporate. The water vapor will then condense on the inner surfaces of the plastic bag, creating droplets. Eventually, you may observe moisture accumulating inside the bag, but the overall amount of liquid water in the cup will remain largely unchanged since the bag is sealed.