Ch.3 - Chemical ReactionsSee all chapters
All Chapters
Ch.1 - Intro to General Chemistry
Ch.2 - Atoms & Elements
Ch.3 - Chemical Reactions
BONUS: Lab Techniques and Procedures
BONUS: Mathematical Operations and Functions
Ch.4 - Chemical Quantities & Aqueous Reactions
Ch.5 - Gases
Ch.6 - Thermochemistry
Ch.7 - Quantum Mechanics
Ch.8 - Periodic Properties of the Elements
Ch.9 - Bonding & Molecular Structure
Ch.10 - Molecular Shapes & Valence Bond Theory
Ch.11 - Liquids, Solids & Intermolecular Forces
Ch.12 - Solutions
Ch.13 - Chemical Kinetics
Ch.14 - Chemical Equilibrium
Ch.15 - Acid and Base Equilibrium
Ch.16 - Aqueous Equilibrium
Ch. 17 - Chemical Thermodynamics
Ch.18 - Electrochemistry
Ch.19 - Nuclear Chemistry
Ch.20 - Organic Chemistry
Ch.22 - Chemistry of the Nonmetals
Ch.23 - Transition Metals and Coordination Compounds
Jules Bruno

The limiting reactant or limiting reagent represents the compound that is totally consumed within a chemical reaction, while the excess reactant represents the compound left over at the end of the chemical process. 

The Theoretical Yield

In order to determine which reactant is the limiting reactant we must calculate the theoretical yield, which represents the maximum amount of product that can possibly made. 

Stoichiometric Chart

In order to determine the theoretical yield of a reaction you must utilize the stoichiometric chart. 

Stoichiometric-Chart-Avogadro-Number-Atoms-Ions-Molecules-Formula-Units-grams-moles-mole-to-mole-comparison-conversionHow to do Stoichiometry (Stoichiometric Chart)

Calculating Theoretical Yield

In order to calculate the theoretical yield of a chemical reaction we will be given the amounts of our reactants and a balanced chemical equation. 

For example, if 21.7 g Al reacts with 34.8 g HBr how many grams of H2 is produced? 

Balanced-Chemical-Equation-Al-HBr-AlBr3-H2-ReactionAl, HBr, AlBr3, H2 Balanced Chemical Equation

STEP 1: Find the atomic masses of the elements from the periodic table. 

Atomic-Masses-Al-H-BrAtomic Masses (Aluminum, hydrogen, bromine)

Do any necessary adding to find the molar masses of Al, HBr and H2

Calculating-Molar-Masses-Al-HBr-H2Calculating Molar Masses (Al, HBr, H2)

STEP 2: Convert the grams of reactants into moles. 

Grams-to-moles-conversions-Al-HBr-Stoichiometry-CalculationGrams to Moles Conversions (Al, HBr)

STEP 3: Convert the moles of reactants to moles of the H2 product by doing mole-to-mole comparisons. 

Balanced-Chemical-Equation-Al-HBr-AlBr3-H2-Single-Displacement-Hydrogen-DisplacementBalanced Chemical Equation (Hydrogen Displacement)

During this step we use the coefficients from the balanced equation. 

Mole-to-Mole-Comparisons-H2Mole to Mole Comparisons (Moles H2)

STEP 4: Convert the moles of H2 into grams of H2

Limiting-Reagent-Worksheet-XR-LR-grams-H2Moles to Grams Conversions (Grams H2)

STEP 5: Determine the theoretical yield. 

The theoretical yield, sometimes referred to as the 100% yield, represents the smaller amount calculated. The theoretical yield is therefore 0.433 g H2

STEP 6: Determine the limiting reactant and the excess reactant. 

The limiting reactant is the compound that gives the smaller amount of product from our calculations, while the excess reactant is the compound that gives the larger amount of product. Therefore HBr is the limiting reactant and Al is the excess reactant. 

Not so limiting

Practice problems dealing with the limiting reactant are very common when dealing with stoichiometry. Stoichiometry itself serves as one of the fundamental concepts you’ll constantly use and connects to other concepts such as mass conversionsempirical formula, percent yield, molarity and solution chemistry

Jules Bruno

Jules felt a void in his life after his English degree from Duke, so he started tutoring in 2007 and got a B.S. in Chemistry from FIU. He’s exceptionally skilled at making concepts dead simple and helping students in covalent bonds of knowledge.