Chapter 9, Problem 33A

Interpretation Introduction

Interpretation:

In a chemical reaction, an excess reactant needs to be explained. Whether a limiting reactant can be present in excess or not needs to be explained. Whether the presence of an excess reactant can affect the mass of the products or not needs to be determined.

Concept Introduction:

• A chemical reaction is represented in terms of a chemical equation with the reactants on the left and the products on the right

  $\text{Reactants }\to \text{ Products}$

• Yield refers to the amount of product formed from a known quantity of the reactants

Answer to Problem 33A

If a certain amount of reactant is left over after the reaction proceeds to completion, then it is said to be present 'in excess'. A limiting reactant is completely used up and cannot be present in excess. The presence of an excess of a reactant does not affect the mass of the products.

Explanation of Solution

Chemical reactions generally proceed when known quantities of reactants combine to form products. The reactants can be present in equal amounts or in varying amounts. If some amount of a particular reactant remains after the reaction is complete, then that reactant is said to be present 'in excess'.

For any given reaction, a limiting reactant is one that is present in the smallest amount (with respect to moles) and is fully consumed during the course of the reaction. Hence they cannot be present in excess.

The reaction yield or the amount of product formed depends only on the limiting reactant since it is the one that gets completely used up. The presence of excess reactant does not affect the mass of the products

Conclusion

Therefore, the maximum yield of a reaction depends on the nature of the limiting reactant which is usually present in the smallest amount.