Final answer:
The reaction of hot sodium with chlorine gas is highly exothermic and produces intense heat and light, resulting in the formation of white sodium chloride crystals.
Step-by-step explanation:
When hot sodium is put into a gas jar of chlorine, a vigorous and exothermic chemical reaction occurs. Initially, the sodium is a shiny metal which quickly reacts upon contact with chlorine, a yellow-green poisonous gas. During the reaction, you would see the sodium metal ignite due to the intense heat produced, and a white bright light might be visible as the sodium loses an electron and chlorine gains it. This is consistent with the reaction being highly exothermic. The reaction produces white sodium chloride (table salt) crystals, and after the reaction has finished, the once reactive sodium and poisonous chlorine have transformed into stable and common table salt. It is important to note these types of reactions should be conducted under controlled conditions due to their violent nature and the generation of heat and light.