Final answer:
UEL or UFL define the highest vapor or gas concentration in the air that can ignite. The heat of vaporization is energy needed to transition from liquid to gas without temperature changes. This knowledge is utilized in processes like separating UF6 isotopes for nuclear fuel.
Step-by-step explanation:
The terms UEL (Upper Explosive Limit) or UFL (Upper Flammability Limit) refer to the highest concentration of vapor or gas in the air that can ignite or explode. When the concentration is above this limit, the gas mixture is too 'rich' to burn. Fire suppression techniques, such as using a fluorinated solution, can help extinguish fires that involve organic liquids by preventing the concentration from reaching flammable levels.
In contrast, the heat of vaporization is the amount of energy needed to convert a substance from a liquid to a gas without a temperature change, which is relevant in various industrial processes, including the gaseous diffusion enrichment plants where UF6 (uranium hexafluoride) is separated based on the molecular weight difference between 235UF6 and 238UF6. This is critical for the functioning of nuclear reactors.