Chemistry Regents Practice Test 2025 – Complete Prep Resource

In a chemical reaction, the limiting reactant is the substance that restricts the extent of the reaction, thereby controlling how much product can be produced. This occurs because the reaction can only proceed until the limiting reactant is completely consumed; once it is used up, no additional product can form, regardless of the amounts of other reactants present.

For example, consider a reaction where one reactant is in excess, and the other is the limiting reactant. The reaction will stop when the limiting reactant runs out, indicating that the theoretical yield of product has been reached based on the stoichiometry of the reactants. This concept is crucial for calculating yields in reactions and understanding the efficiency of reagent usage in various chemical processes.

In contrast, the other options do not correctly describe the role of the limiting reactant in a reaction. Limiting reactants do not influence the temperature, are not defined by being consumed last, and do not have any direct effect on the activation energy of the reaction.