Final answer:
The propagating step in a chain reaction is when reactive intermediates react with stable molecules to create new intermediates, continuing the reaction. In the H₂ and O₂ reaction to form H₂O, this step involves free radicals reacting with molecules continuously to create water. This propagation process is essential in the overall chain reaction, allowing it to sustain itself.
Step-by-step explanation:
The propagating step in a chain reaction refers to the sequence in which highly reactive intermediates (often free radicals) react with stable molecules to produce new free radicals, perpetuating the reaction process. In the context of mixing hydrogen (H₂) and oxygen (O₂) to form water (H₂O), each H₂ molecule can react with an O₂ molecule to form two H₂O molecules. However, this simplified view overlooks the chain mechanism that actually occurs during the reaction.
For instance, if we consider the breakdown of hydrogen peroxide as an example, the propagation step involves a free radical created in the initiation step reacting with another H₂O₂ molecule, forming water and another free radical, which can then react further with additional hydrogen peroxide molecules. This set of steps keeps the chain reaction going. The overall balanced chemical equation for the formation of water is 2H₂(g) + O₂(g) → 2H₂O(l), where (g) signifies that the hydrogen and the oxygen are in the gaseous state, and (l) signifies that the water produced is in the liquid state.
In the educational tool described, where H₂ and O₂ units are placed on a table representing a test tube, the breaking and reforming of bonds can be simulated to illustrate the ongoing nature of the propagation steps in the reaction to form water molecules.