A tightly closed metal lid of a glass bottle can be opened more easily if it is put in hot water for some time because coefficient of expansion of metal is greater than that of glass. So, when the metal lid comes in contact with hot water, it expands at a faster rate than the glass jar, which in turn forms a gap between the metal lid and the glass bottle. This gap increases as the metal lid expands, as a result glass bottle can be opened more easily.