Final answer:
The reaction of ethanol with oxygen to form carbon dioxide and water will occur most rapidly when ethanol and oxygen are in close contact, as this increases the frequency and energy of collisions between reactant molecules.
Step-by-step explanation:
The reaction in question, C₂H₅OH + 3O₂ ⎯→ 2CO₂ + 3H₂O, will occur most rapidly under certain conditions. For a combustion reaction like this, where ethanol (C₂H₅OH) reacts with oxygen (O₂) to form carbon dioxide (CO₂) and water (H2O), the most important factor in determining the rate of reaction is the frequency and energy of successful collisions between the reactant molecules.
Choice b, where C₂H₅OH and O₂ are in close contact, will facilitate more frequent collisions, and therefore, the reaction will likely proceed at a faster rate. In contrast, when one or both reactants are in a liquid state, as suggested in choice a, their molecules will not collide as frequently or energetically, slowing down the reaction. The physical states of the products, as in choices c and d, do not generally affect the rate of the initial reaction.