Undergraduate
  1. General chemistry  1.1. Introduction to Chemistry  1.2. Atomic Structure  1.2.1. Subatomic particles  1.2.2. Atomic Model  1.2.3. Quantum numbers  1.2.4. Electron Configuration  1.2.5. Periodic trends  1.2.6. Isotopes and their applications  1.3. Chemical bond  1.3.1. Ionic bond  1.3.2. Covalent bonds  1.3.3. Metal Bond  1.3.4. Hybridization  1.3.5. Molecular geometry and VSEPR theory  1.3.6. Bond polarity and dipole moment  1.4. Stoichiometry  1.4.1. Mole concept  1.4.2. Empirical and molecular formula  1.4.3. Limiting reactant and excess reactant  1.4.4. Percent Yield and Purity  1.4.5. Dilution calculation  1.5. States of matter  1.5.1. Gas Laws  1.5.2. Matter and Intermolecular Forces  1.5.3. Solid and Crystal Structures  1.5.4. Phase diagram  1.5.5. Plasma and supercritical fluid  1.6. Chemical reactions  1.6.1. Types of Chemical Reactions  1.6.2. Balancing Chemical Equations  1.6.3. Thermochemical reactions  1.6.4. Reaction energy profiles  1.7. Solutions and Mixtures  1.7.1. Concentration units  1.7.2. Syndrome properties  1.7.3. Solubility and Solubility Rules  1.7.4. Henry's Law and Raoult's Law  1.7.5. Partition coefficient  1.8. Chemical equilibrium  1.8.1. Law of mass action  1.8.2. Le Chatelier's principle  1.8.3. Reaction quotient  1.8.4. To use this online calculator for Equilibrium Constant, enter Equilibrium Constant (Eq.) and hit the calculate button. Here is how the Equilibrium Constant calculation can be explained with given input values -> 0.05 = 0.05/0.  1.8.5. Acid-base balance  1.9. Acids and bases  1.9.1. Arrhenius, Brønsted–Lowry, and Lewis definitions  1.9.2. pH and pOH  1.9.3. Acid-base titration  1.9.4. Buffer Solution  1.9.5. Acid-base indicator  1.9.6. Polyprotic Acids and Bases  1.10. Electrochemistry  1.10.1. redox reactions  1.10.2. Galvanic and Electrolytic Cells  1.10.3. Nernst equation  1.10.4. Electrolysis  1.10.5. Faraday's laws of electrolysis  1.11. Thermodynamics  1.11.1. Laws of Thermodynamics  1.11.2. Enthalpy, entropy and Gibbs free energy  1.11.3. Spontaneity of reactions  1.11.4. Thermodynamic cycles (Hess's law, Carnot cycle)  1.12. Kinetics  1.12.1. Rate law and reaction order  1.12.2. Activation Energy and Catalyst  1.12.3. Collision theory  1.12.4. Reaction mechanism  1.12.5. Transition state theory
  2. Organic chemistry  2.1. Structure and relationships  2.1.1. Hybridisation in Carbon Compounds  2.1.2. Resonance and aromatization  2.1.3. Molecular orbitals  2.1.4. Inductive and mesomeric effects  2.2. Hydrocarbons  2.2.1. Hydrocarbons  2.2.2. Alkene  2.2.3. Alkynes  2.2.4. Aromatic compounds  2.2.5. Cycloalkanes and Conformation  2.3. Functional Group  2.3.1. Alcohols and phenols  2.3.2. Ethers and epoxides  2.3.3. Aldehyde and ketone  2.3.4. Carboxylic acids and derivatives  2.3.5. Amin  2.3.6. Esters and amides  2.3.7. Thiols and sulfides  2.4. Stereoscopic  2.4.1. Isomerism in Stereochemistry  2.4.2. Chirality and optical activity  2.4.3. Structural analysis  2.4.4. Diastereomers and Enantiomers  2.5.1. Substitution reactions  2.5.2. Elimination reactions  2.5.3. Addition reactions  2.5.4. Radical reactions  2.5.5. Rearrangement reactions  2.5.6. Pericyclic Reactions  2.6. Spectroscopy and structural analysis  2.6.1. Infrared Spectroscopy  2.6.2. Nuclear magnetic resonance spectroscopy  2.6.3. Mass Spectrometry  2.6.4. UV-visible spectroscopy  2.6.5. X-ray crystallography  2.7. Polymer chemistry  2.7.1. Addition and Condensation Polymers  2.7.2. Polymerization mechanism  2.7.3. Biodegradable Polymer  2.7.4. Conducting and smart polymers
  3. Inorganic chemistry  3.1. Coordination chemistry  3.1.1. Ligands and coordination compounds  3.1.2. Crystal field theory  3.1.3. Molecular Orbital Theory in Coordination Compounds  3.1.4. Jahn–Taylor distortion  3.2. Main Group Chemistry  3.2.1. Alkali and alkaline earth metals  3.2.2. Halogens and Noble Gases  3.2.3. Transition metals and their complexes  3.2.4. Lanthanides and Actinides  3.3. Solid state chemistry  3.3.1. Crystal lattices and unit cells  3.3.2. Defects in solids  3.3.3. Electrical and magnetic properties  3.3.4. Superconductivity  3.4. Bio-inorganic chemistry  3.4.1. Metal ions in biology  3.4.2. Enzymatic reactions with metals  3.4.3. Metal poisoning and detoxification  3.4.4. Metalloproteins and Metalloenzymes
  4. Physical chemistry  4.1. Quantum Chemistry  4.1.1. Wave–particle duality  4.1.2. Schrödinger Equation  4.1.3. Quantum Numbers and Orbitals  4.1.4. Atomic and molecular spectroscopy  4.2. Statistical mechanics  4.2.1. Maxwell–Boltzmann distribution  4.2.2. Partitioning functions  4.2.3. Bose–Einstein and Fermi–Dirac statistics  4.3. Chemical thermodynamics  4.3.1. Gibbs Free Energy  4.3.2. Phase transition  4.3.3. Thermodynamic efficiency  4.4. Surface chemistry  4.4.1. Absorption and Catalysis  4.4.2. Colloids and Emulsions
  5. Analytical Chemistry  5.1. Classical methods  5.1.1. Gravimetric Analysis  5.1.2. titrimeter  5.2. Instrumental methods  5.2.1. Chromatography  5.2.2. Spectroscopy  5.2.3. Electroanalytical methods  5.2.4. X-ray diffraction
  6. Industrial Chemistry  6.1. Petrochemistry  6.2. Chemical engineering principles  6.3. Green Chemistry  6.4. Pharmaceuticals and Drug Synthesis
  7. Biochemistry  7.1. Carbohydrates  7.2. Proteins and enzymes  7.3. Lipids and membranes  7.4. Nucleic acids  7.5. Metabolism and Bioenergetics  7.6. Enzyme kinetics and mechanism

Undergraduate → General chemistry → Stoichiometry ↓


Limiting reactant and excess reactant


In the world of chemistry, the concept of limiting reactants and excess reactants is fundamental to understanding reactions and their outcomes. This topic is important for predicting how much product will be formed in a chemical reaction. Let's delve deeper into this concept by exploring detailed explanations, examples, and exercises.

Understanding the basics

When substances react chemically, they do so according to particular stoichiometric ratios determined by the balanced chemical equation of the reaction. These ratios determine how much of each substance is needed to completely react with the others.

However, in practical scenarios, the reactants are not always present in exact stoichiometric quantities. One reactant is often used before the others, and this reactant is known as the limiting reactant. The limiting reactant determines the maximum amount of product that can be formed in the reaction.

Defining limiting and excess reactants

Limiting reactant

The limiting reactant is the substance that is completely used up in a chemical reaction. The reaction cannot proceed once the limiting reactant is used up, and therefore, it limits the amount of product that can be formed.

Excess reactant

Excess reactant is the substance that is left after the reaction is complete. The amount of this reactant is more than what is needed to completely react with the limiting reactant.

Illustrative analogy: making a sandwich

To make this concept more clear, let's take a simple example of making a sandwich. Suppose you are making a sandwich with the following ingredients:

  • Bread crumbs
  • Cheese slices
  • Ham slices

Let's say to make a complete sandwich you need:

  • 2 bread slices
  • 1 slice of cheese
  • 1 ham slice

Here are the things you should have in your pantry:

  • Bread slices: 10
  • Paneer pieces: 4
  • Ham slices: 6

In this scenario, the cheese slices are the limiting factor because you can only make 4 full sandwiches, which is limited by the lack of cheese available. Bread and ham are extra.

Reaction example

Consider the chemical reaction between nitrogen gas (N 2) and hydrogen gas (H 2) to produce ammonia (NH 3):

    N 2 + 3H 2 → 2NH 3

If you start with 1 mole of nitrogen gas and 4 moles of hydrogen gas, identify the limiting reactant and the amount of ammonia produced.

Step 1: Calculate the moles required

  • From the equation, 1 mole of N 2 requires 3 moles of H 2.
  • You have 4 moles of H 2 available.

Step 2: Determine the limiting reactant

  • To react with 1 mole of N 2, you need 3 moles of H 2, leaving 1 mole of H 2 unreacted.
  • N 2 is the limiting reactant.

Step 3: Calculate the product manufactured

  • Using the balanced equation: 1 mol N 2 yields 2 mol NH 3.
  • The amount of ammonia formed is 2 mol.

How to identify the limiting reactant

The method for finding the limiting reactant involves comparing the mole ratio of the reactants used in the actual mixture to the mole ratio in the balanced equation. Here's a step-by-step guide:

  1. Write the balanced equation for the reaction.
  2. Convert the amounts of available reactants into moles.
  3. Use the balanced equation to determine the stoichiometric ratio of reactants.
  4. Calculate the theoretical amount of each reactant needed to react completely with the other reactants.
  5. Identify the reactant that will be used first—this is your limiting reactant.

Example

Let's look at an example of making aluminum chloride (AlCl 3) from the reaction between aluminum (Al) and chlorine gas (Cl 2), with the balanced equation:

    2Al + 3Cl 2 → 2AlCl 3

You have 5 moles of aluminum and 6 moles of chlorine gas. To find the limiting reactant, do the following:

Step-by-step calculation

Step 1: Acquire comparison

  • According to the equation, 2 moles of Al react with 3 moles of Cl 2.

Step 2: Determine reactant needed

  • To completely react 5 moles of Al you need: 
                (5 moles Al) * (3 moles Cl₂ / 2 moles Al) = 7.5 moles Cl₂
  • Since you only have 6 moles Cl 2, Cl 2 is the limiting reactant.

Step 3: Calculate product manufacturing

  • From 6 moles of Cl 2 is formed: 
                (6 mol Cl₂) * (2 mol AlCl₃ / 3 mol Cl₂) = 4 mol AlCl₃

Importance in industrial chemistry

In industrial chemistry and manufacturing, determining the limiting reactant is essential for economical and efficient production. Using the correct ratio of reactants can save costs and reduce waste.

  • This ensures that expensive reactants are not wasted.
  • Helps to scale up the reaction from laboratory to industrial scale.
  • Helps protect the environment by minimizing chemical waste.

Practice problems

Try solving the following problems to reinforce your understanding:

  1. For the combustion of propane (C 3 H 8), the balanced equation is: 
            C 3 H 8 + 5O 2 → 3CO 2 + 4H 2 O
    You have 5 moles of C 3 H 8 and 18 moles of O 2 Identify the limiting reactant.
  2. In the synthesis of water, H 2 + O 2 → H 2 O, starting with 3 moles of H 2 and 5 moles of O 2, what is the limiting reactant, and how many moles of water are produced?

Conclusion

Understanding limiting and excess reactants in stoichiometry is important for predicting product formation and optimizing chemical reactions. By mastering this concept, you will be able to solve complex chemical problems with confidence.


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Limiting reactant and excess reactant

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