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


Stoichiometry is a fundamental concept in chemistry that deals with the quantitative relationships between reactants and products in a chemical reaction. It provides a measure for understanding how substances combine and react with each other in specific proportions. This knowledge is important for both theoretical predictions and practical applications in laboratories and industries.

Understanding stoichiometry

The term stoichiometry is derived from the Greek words stoicheion (element) and metron (measurement). It involves calculating the amounts of reactants and products in a chemical reaction using a balanced chemical equation.

Example:
 
Consider the simple combustion reaction of hydrogen and oxygen to form water:
H 2 + O 2 → H 2 O

The balanced form of this chemical equation is:

2H 2 + O 2 → 2H 2 O

In a balanced chemical equation, the number of atoms of each element involved in the reaction is the same on both the reactant and product sides. This is in accordance with the law of conservation of mass, which states that matter cannot be created or destroyed in an isolated system.

Mole concept

The mole is a fundamental unit in chemistry that serves as a bridge between the atomic and macroscopic scales. One mole of any substance contains Avogadro's number of particles (atoms, molecules, ions, etc.), which is approximately (6.022 x 10^{23}). The mole concept is important in stoichiometry because it allows chemists to convert between the mass of a substance and the number of particles or entities it contains.

To illustrate:

1 mole of carbon atoms = (6.022 x 10^{23}) carbon atoms

1 mole of H 2 O molecules = (6.022 x 10^{23}) H 2 O molecules

Molar mass is another essential idea related to the mole concept. It is the mass of one mole of a substance, usually expressed in grams per mole (g/mol). The molar mass of an element is numerically equal to its atomic mass in unified atomic mass units (u).

How to write and balance a chemical equation

Writing and balancing chemical equations is an important skill in stoichiometry. A chemical equation uses chemical formulas to give the 'recipe' of a chemical reaction, showing the reactants and products, their physical states, and the amounts of each substance involved.

Here's how to write and balance a chemical equation:

1. Write the unbalanced equation using the correct chemical formulas and states of matter. 2. Count the number of atoms of each element on both the reactant and product sides. 3. Use coefficients to balance each element. 4. Make sure all coefficients are in the smallest possible whole number ratio.

Example:

Unbalanced:
C 4 H 10 + O 2 → CO 2 + H 2 O

Balanced:
2C 4 H 10 + 13O 2 → 8CO 2 + 10H 2 O

In this balanced equation, we can see that the same number of each type of atom appears on both sides of the equation. This observance of the law of conservation of mass proves that your stoichiometric calculation is on the right track.

Using stoichiometry: Step-by-step calculations

Stoichiometric calculations follow the following steps:

1. Identify the information given

Determine what quantities you know (mass, moles, volume), such as grams of a substance, and what you need to determine.

2. Write and balance the equation

Make sure the chemical equation for the reaction is balanced, and note the molar ratios of the reactants and products. These ratios will be important for calculations.

3. Convert units to moles

Convert all known quantities to moles if they aren't already. Use molar mass for this conversion.

4. Use the mole ratio

Apply the mole ratio from the balanced equation to relate moles of one substance to the corresponding amounts of another substance.

5. Convert moles to desired units

Finally, convert the moles of the unknown quantity to the desired units, often mass or volume. Use molar volume or molar mass as needed.

Example:

Given the balanced equation:
2H 2 + O 2 → 2H 2 O

Suppose you want to calculate how many grams of water will be formed from 5 grams of hydrogen.

Step 1: Calculate the moles of H2:
n(H2) = mass / molar mass = 5 g / 2.02 g/mol = 2.475 mol H2
   
Step 2: Use the mole ratio (from the balanced equation: 2 moles of H 2: 2 moles of H 2 O):
n(H 2 O) = n(H 2) = 2.475 mol H 2 O
   
Step 3: Convert moles of H 2 O to grams:
mass(H 2 O) = n(H 2 O) * molar mass = 2.475 mol * 18.02 g/mol = 44.57 g H 2 O

Limiting reactant

In chemical reactions, the limiting reactant (or limiting reagent) is the substance that is completely consumed and thus limits the amount of product formed. This concept is important in determining the theoretical yield of a reaction.

Example:

Given the balanced equation:
2Al + 3Cl 2 → 2AlCl 3

Suppose you have 5 moles of Al and 8 moles of Cl 2. Which is the limiting reactant?

Step 1: Determine the mole ratio from the equation: 
2 moles of Al react with 3 moles of Cl 2.

Step 2: Use the ratio to calculate the needed amount of another reactant:
Moles of Cl 2 required for 5 moles of Al = (3/2) * 5 = 7.5 moles

Step 3: Compare with the amount of Cl 2 available:
You have 8 moles of Cl 2. Therefore, Al is the limiting reactant because 5 moles would require 7.5 moles of Cl 2.

The limiting reactant determines the maximum amount of product formed in a reaction, and the remaining reactants are considered to be in excess.

Theoretical yield, actual yield, and percent yield

The theoretical yield is the amount of product that would be obtained if the reaction were 100% efficient, based solely on stoichiometric calculations.

Actual yield is the amount of product actually obtained from an experiment or process.

Percent yield is a measure of the efficiency of a reaction and is calculated using the following formula:

Percentage yield = (actual yield / theoretical yield) * 100

Example:

If the theoretical yield of a product is 10 g but only 8 g are produced, the percent yield is:
Percentage yield = (8 g / 10 g) * 100 = 80%

Stoichiometry in everyday life

Stoichiometry is not just confined to the laboratory. It plays a vital role in a variety of real-life applications, from making informed decisions in cooking recipes to understanding combustion efficiency in engines. Its principles are important in agriculture to determine the required amount of fertilizers or pesticides, and in environmental science to analyze pollutant levels.

Challenges and common mistakes

  • Failure to balance the chemical equation correctly can result in incorrect calculations.
  • Error in conversion from grams to moles or vice versa.
  • Incorrect determination of the limiting reactant, which affects calculation of the theoretical yield.
  • Not considering significant figures in calculations, especially when considering experimental data.

In conclusion, mastering stoichiometry is essential for any chemistry student as it is fundamental in understanding and performing chemical reactions. An understanding of key concepts such as step-by-step method of calculation, moles, molar mass, and balanced equations are crucial to effectively analyze and predict the outcomes of chemical reactions.

By practicing stoichiometry problems and applying these principles, it becomes possible to gain proficiency in stoichiometry. This is a skill that develops a deep understanding for the accuracy and logic that underlies chemical science.


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Stoichiometry

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