Hello, Please forgive my ignorance, although bright, I was a lousy student, & never took physics in school. I find it frustrating when relatives & friends are uncertain as to how to respond to questions like those below, so your educated reply would therefore be all the more appreciated. Thank you. I would assume that frozen H20 completely filling the space of a closed system would convert to water if the container (one whose walls consisted of an energy conductor such as aluminum) would be placed in an environment above 0 Celsius, since extra room is not required for the newly formed water, as water is denser than ice. However, the converse, would probably not be true, as when placing the same container, this time filled completely with water in a room where the temperature is below 0 Celsius, since the water would have no room to expand when attempting to convert to a solid. Similarly, I would assume that dry ice completely filling a container, as the one described above, would not sublimate, when the container is placed in a room above -78.5 degrees Celsius. I understand that in the dry ice example, the container's walls would have to be sufficiently thick to offset the increasing pressure buildup resulting from sublimation. But if the inside of the container were, say, one square foot, and the walls of the container would be a foot thick, and instead of aluminum have the walls of the container made of titanium, would the dry ice sublimate without risk of explosion or would the pressure buildup not allow the dry ice to sublimate?