Question 1

What is the limiting reagent?

Accepted Answer

The limiting reagent is the reactant that is completely consumed first in a chemical reaction, determining the maximum amount of product that can be formed. All other reagents are described in terms of equivalents relative to the limiting reagent.

Question 2

How do you calculate percent yield?

Accepted Answer

Percent yield = (actual yield / theoretical yield) × 100. The theoretical yield is calculated from the moles of limiting reagent and the product molecular weight. Yields above 100% indicate an error such as impure product or incorrect molecular weight.

Question 3

What is atom economy?

Accepted Answer

Atom economy measures the efficiency of a reaction by comparing the molecular weight of the desired product to the total molecular weight of all products. Higher atom economy means less waste. Addition reactions approach 100% atom economy while substitutions and eliminations are typically lower.

Question 4

How do equivalents work in organic chemistry?

Accepted Answer

Equivalents express the molar ratio of a reagent relative to the limiting reagent. 1.0 equiv means equimolar. Reagents are often used in slight excess (1.1–1.5 equiv) to drive the reaction to completion. Catalysts are described in mol% instead of equivalents.

Question 5

Where can I find molecular weights?

Accepted Answer

PubChem (pubchem.ncbi.nlm.nih.gov) is the most reliable free source for molecular weights. Search by compound name, CAS number, or structure. For salt forms and hydrates, use the molecular weight of the specific form you are weighing, not the free base.

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