Only very specific types of material completely freeze, melt, condense or vaporize in a reversible way when their temperature changes. Mostly simple chemical structures that consist entirely of a single type of molecule, single elements or a mixture of elements that aren’t chemically bonded together.
Most materials are far more complex than that and will undergo chemical changes to their structure on heating instead. They may break down, change their structure, lose small molecules as gas, react with moisture or oxygen. Even some quite simple molecules aren’t stable enough to reach a point where they would melt, decomposing instead. Baking soda, sodium bicarbonate, for instance which loses carbon dioxide when heated.
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