When heat is supplied to a substance, its internal energy increases. Typically, this leads to an increase in temperature. However, if the substance is undergoing a phase change (like melting from solid to liquid or boiling from liquid to gas), the added heat is used to change the state rather than increase the temperature. During a phase transition at constant pressure, the temperature remains constant while heat is absorbed. Metals, like other substances, undergo melting and boiling at specific temperatures if sufficient heat is supplied.