in a vacuum water would sublimate when heated up without ever going through the liquid phase first. As I understand it intuitively, this is because up to melting temperature, the heat energy goes into separating the molecules from their bonds, but it is the air pressure that then prevent them from just flying off. which means they start swimming among each other without yet being able to escape the downward push force of the atmospheric air pressure.
So adding enough heat to increase the temperature by 100 deg C, is then what is needed to give the molecules enough energy to overcome the air pressure and turn into gas (boil. I know some turn into gas before that temp.). Is this understanding correct?
If it is correct. My main question is this; if water is able to fight atm. Air pressure with only a 100 deg C difference in temp/energy. Why does a metal for instance need a temperature/energy difference from 1500 deg C (melting) to 2500 deg C (boil) in order to counter the same atm. air pressure and become a gas?