Question

What does it mean to say a reactant is present "in excess" in a process? Can the limiting reactant be present in excess? Does the presence of an excess of a reactant affect the mass of products expected for a reaction?

Short answer

A reactant is present "in excess" if there is more of it than required to completely react with the other reactant(s). A limiting reactant, which determines the maximum amount of product that can be formed, cannot be present in excess. The presence of a reactant in excess does not affect the mass of the products expected in the reaction, but it ensures that the limiting reactant is fully utilized and can influence the completion of the reaction.

Step-by-step solution

Defining Reactants in Excess and Limiting Reactants

In a chemical reaction, a reactant is considered to be in excess if there is more of that substance than required to completely react with the other reactant(s) present. On the other hand, the limiting reactant is the reactant that is completely consumed during the reaction and determines the maximum amount of product that can be formed.

Is Limiting Reactant Present in Excess

By definition, a limiting reactant cannot be present in excess. It is the one that determines the extent of the reaction, while reactants in excess are present in greater amounts than necessary for the reaction to reach completion.

Effect of Excess Reactants on Product Mass

The presence of a reactant in excess does not affect the mass of products expected in the reaction. As the limiting reactant dictates the amount of product formed, any additional reactant in excess will not contribute to producing more products. However, the presence of excess reactants can ensure that the limiting reactant is fully utilized and can influence the completion of the reaction.