Complete Chemistry Reactions Cheatsheet: Types, Mechanisms & Applications

Introduction to Chemical Reactions

Chemical reactions are processes where substances (reactants) transform into different substances (products) through the breaking and forming of chemical bonds. Understanding reaction types and mechanisms is fundamental to chemistry and enables predictions about how substances interact. This cheatsheet provides a comprehensive reference for identifying, balancing, and applying common chemical reactions across organic and inorganic chemistry.

Fundamental Concepts

Components of a Chemical Reaction

• Reactants: Starting substances consumed in the reaction
• Products: New substances formed by the reaction
• Coefficients: Numbers preceding formulas that balance the equation
• Reaction Arrow: Indicates direction of reaction (→, ⇌, ⇄)
• Conditions: Temperature, pressure, catalysts, etc. (often shown above or below arrow)

Balancing Chemical Equations

1. Identify all elements present in the reaction
2. Balance elements one at a time (typically start with most complex molecules)
3. Verify that atoms of each element are equal on both sides
4. Use fractional coefficients for half-reactions if needed, then multiply to get whole numbers

Reaction Yield Calculations

• Theoretical Yield: Maximum amount of product possible based on limiting reactant
• Actual Yield: Amount of product actually obtained experimentally
• Percent Yield: (Actual Yield ÷ Theoretical Yield) × 100%
• Limiting Reactant: Reactant that determines the maximum amount of product

Types of Inorganic Reactions

Combination/Synthesis Reactions

General Form: A + B → AB

Decomposition Reactions

General Form: AB → A + B

Single Replacement/Displacement Reactions

General Form: A + BC → AC + B

Activity Series of Metals (decreasing reactivity): Li > K > Ba > Sr > Ca > Na > Mg > Al > Mn > Zn > Cr > Fe > Cd > Co > Ni > Sn > Pb > H > Cu > Ag > Hg > Au

Activity Series of Halogens (decreasing reactivity): F₂ > Cl₂ > Br₂ > I₂

Double Replacement/Displacement Reactions

General Form: AB + CD → AD + CB

Combustion Reactions

General Form: Fuel + O₂ → CO₂ + H₂O (+ energy)

Oxidation-Reduction (Redox) Reactions

Key Concepts:

• Oxidation: Loss of electrons (increase in oxidation number)
• Reduction: Gain of electrons (decrease in oxidation number)
• Oxidizing Agent: Gets reduced and causes oxidation of another substance
• Reducing Agent: Gets oxidized and causes reduction of another substance

Common Oxidizing Agents:

• KMnO₄ (potassium permanganate)
• K₂Cr₂O₇ (potassium dichromate)
• H₂O₂ (hydrogen peroxide)
• HNO₃ (nitric acid)
• O₂ (oxygen)
• F₂, Cl₂, Br₂, I₂ (halogens)

Common Reducing Agents:

• Metals (Na, Mg, Zn, Fe, Al)
• H₂ (hydrogen)
• CO (carbon monoxide)
• C (carbon)
• SO₂ (sulfur dioxide)
• Na₂S₂O₃ (sodium thiosulfate)

Balancing Redox Reactions in Acidic Solution:

1. Write skeletal equation
2. Split into half-reactions
3. Balance elements other than O and H
4. Balance O using H₂O
5. Balance H using H⁺
6. Balance charge using electrons
7. Equalize electrons transferred in both half-reactions
8. Add half-reactions
9. Cancel identical species

Balancing Redox Reactions in Basic Solution:

1. Follow steps 1-7 for acidic solution
2. Add OH⁻ to both sides to neutralize H⁺ (for each H⁺, add one OH⁻)
3. Form H₂O where H⁺ and OH⁻ appear on same side
4. Cancel identical species

Acid-Base Reactions

Acid-Base Theories

Conjugate Acid-Base Pairs

• Conjugate acid: Formed when a base gains a proton
• Conjugate base: Formed when an acid loses a proton

Examples:

• HCl (acid) → H⁺ + Cl⁻ (conjugate base)
• NH₃ (base) + H⁺ → NH₄⁺ (conjugate acid)

Acid-Base Strength

Relative Strength of Acids:

1. Hydrohalic acids: HI > HBr > HCl > HF
2. Oxoacids: Strength increases with:
   • More oxygen atoms: HClO₄ > HClO₃ > HClO₂ > HClO
   • More electronegative central atom: H₂SO₄ > H₂SeO₄

Relative Strength of Bases:

1. Alkali metal hydroxides: LiOH < NaOH < KOH < RbOH < CsOH
2. Organic amines: NH₃ < CH₃NH₂ < (CH₃)₂NH < (CH₃)₃N

Ka and Kb Values:

• Strong acids: Ka > 1 (HCl, HNO₃, H₂SO₄, HBr, HI, HClO₄)
• Weak acids: Ka < 1 (CH₃COOH, HF, H₂CO₃, HNO₂)
• Strong bases: Kb > 1 (NaOH, KOH, Ca(OH)₂, Ba(OH)₂)
• Weak bases: Kb < 1 (NH₃, organic amines)

Precipitation Reactions & Solubility Rules

General Solubility Rules

Common Ion Effect & Solubility Product (Ksp)

• Ksp: Product of concentrations of ions in a saturated solution
• Common Ion Effect: Decreases solubility when a common ion is added

Example:

• For AgCl ⇌ Ag⁺ + Cl⁻, Ksp = [Ag⁺][Cl⁻]
• Adding NaCl decreases AgCl solubility by increasing [Cl⁻]

Complexation Reactions

Formation of Complex Ions

• Ligands: Electron pair donors that bind to metal ions
• Coordination Number: Number of donor atoms bound to central metal ion

Common Ligands:

• Monodentate: H₂O, NH₃, CN⁻, Cl⁻, OH⁻
• Bidentate: C₂O₄²⁻ (oxalate), H₂NCH₂CH₂NH₂ (ethylenediamine)
• Polydentate: EDTA⁴⁻

Examples:

• Cu²⁺ + 4NH₃ → [Cu(NH₃)₄]²⁺ (tetraamminecopper(II))
• Fe³⁺ + 6CN⁻ → [Fe(CN)₆]³⁻ (hexacyanoferrate(III))

Complex Ion Equilibria

• Formation Constant (Kf): Measures stability of complex ion
• Higher Kf = more stable complex

Example:

• For Ag⁺ + 2NH₃ ⇌ [Ag(NH₃)₂]⁺, Kf = [[Ag(NH₃)₂]⁺]/([Ag⁺][NH₃]²)

Organic Reactions

Substitution Reactions

Nucleophilic Substitution (SN)

Electrophilic Aromatic Substitution (EAS)

Effect of Substituents on EAS:

• Activating groups (increase reaction rate): -NH₂, -NHR, -NR₂, -OH, -OR, -R
• Deactivating groups (decrease reaction rate): -NO₂, -CN, -SO₃H, -COOH, -CHO, -COR, -COOR, -NH₃⁺
• Ortho/para directors: -NH₂, -NHR, -NR₂, -OH, -OR, -R, -X (halogens)
• Meta directors: -NO₂, -CN, -SO₃H, -COOH, -CHO, -COR, -COOR, -NH₃⁺

Addition Reactions

Addition to Alkenes

Markovnikov’s Rule: In addition of HX to alkene, H attaches to carbon with more hydrogen atoms, X to carbon with fewer hydrogen atoms

Anti-Markovnikov Addition: Occurs in hydroboration-oxidation (H attaches to carbon with fewer hydrogen atoms)

Elimination Reactions

Zaitsev’s Rule: In elimination reactions, the major product is the more substituted alkene (more stable)

Condensation Reactions

Redox Reactions in Organic Chemistry

Polymerization Reactions

Addition Polymerization

• Mechanism: Monomers with double bonds join end-to-end
• Examples:
  • Ethylene → Polyethylene: n(CH₂=CH₂) → -(CH₂-CH₂)ₙ-
  • Styrene → Polystyrene: n(CH₂=CH-C₆H₅) → -(CH₂-CH(C₆H₅))ₙ-
  • Vinyl chloride → PVC: n(CH₂=CHCl) → -(CH₂-CHCl)ₙ-

Condensation Polymerization

• Mechanism: Monomers join with loss of small molecules (H₂O, HCl, etc.)
• Examples:
  • Nylon 6,6: n(HOOC-(CH₂)₄-COOH) + n(H₂N-(CH₂)₆-NH₂) → -[OC-(CH₂)₄-CO-NH-(CH₂)₆-NH]ₙ- + 2nH₂O
  • Polyester (PET): n(HOOC-C₆H₄-COOH) + n(HO-CH₂-CH₂-OH) → -[OC-C₆H₄-CO-O-CH₂-CH₂-O]ₙ- + 2nH₂O

Electrochemical Reactions

Galvanic/Voltaic Cells

• Anode: Oxidation occurs (electrons generated)
• Cathode: Reduction occurs (electrons consumed)
• Example: Zn|Zn²⁺||Cu²⁺|Cu
  • Anode (oxidation): Zn → Zn²⁺ + 2e⁻
  • Cathode (reduction): Cu²⁺ + 2e⁻ → Cu

Electrolytic Cells

• Anode: Oxidation occurs (electrons leave cell)
• Cathode: Reduction occurs (electrons enter cell)
• Example: Electrolysis of molten NaCl
  • Anode (oxidation): 2Cl⁻ → Cl₂ + 2e⁻
  • Cathode (reduction): 2Na⁺ + 2e⁻ → 2Na

Nernst Equation

• E = E° – (RT/nF)ln(Q)
• At 25°C: E = E° – (0.0592/n)log(Q)
• E° = standard cell potential
• n = number of electrons transferred
• Q = reaction quotient

Nuclear Reactions

Types of Nuclear Decay

Nuclear Equations

• Fission: ₂₃₅U + ₁n → ₁₄₁Ba + ₉₂Kr + 3₁n + energy
• Fusion: ₂H + ₃H → ₄He + ₁n + energy

Chemical Kinetics

Rate Laws

• First-Order: Rate = k[A], t₁/₂ = 0.693/k
• Second-Order: Rate = k[A]², t₁/₂ = 1/(k[A]₀)
• Zero-Order: Rate = k, t₁/₂ = [A]₀/2k

Determining Reaction Order

• Method of Initial Rates: Compare rates at different initial concentrations
• Integrated Rate Law Plots:
  • First-Order: ln[A] vs t gives straight line
  • Second-Order: 1/[A] vs t gives straight line
  • Zero-Order: [A] vs t gives straight line

Factors Affecting Reaction Rate

• Temperature: Higher T → faster rate (Arrhenius equation)
• Catalysts: Lower activation energy → faster rate
• Concentration: Higher conc. → faster rate (except zero-order)
• Surface Area: More SA → faster rate
• Pressure: Higher P → faster rate (for gaseous reactions)

Reaction Mechanisms & Intermediates

Common Reaction Intermediates

Multi-Step Reaction Mechanisms

• Rate-Determining Step: Slowest step that determines overall rate
• Steady-State Approximation: Intermediates consumed as quickly as formed

Spectroscopic Analysis of Reactions

IR Spectroscopy Functional Group Identification

NMR Spectroscopy in Reaction Monitoring

• ¹H NMR: Tracks changes in proton environments
• ¹³C NMR: Monitors carbon skeleton changes
• Time-resolved NMR: Follows reaction kinetics in real-time

Green Chemistry & Sustainable Reactions

Principles of Green Chemistry

1. Prevention: Better to prevent waste than treat it
2. Atom Economy: Maximize incorporation of reactants into final product
3. Safer Reagents: Use less hazardous chemical synthesis
4. Design Safer Chemicals: Maintain efficacy while reducing toxicity
5. Safer Solvents: Use safer solvents and auxiliaries
6. Energy Efficiency: Minimize energy requirements
7. Renewable Feedstocks: Use renewable raw materials
8. Reduce Derivatives: Minimize or avoid derivatization
9. Catalysis: Catalytic reagents superior to stoichiometric reagents
10. Degradation: Design for degradation
11. Real-time Analysis: Real-time monitoring for pollution prevention
12. Accident Prevention: Minimize potential for accidents

Sustainable Reaction Examples

• Aqueous-phase reactions: Replaces organic solvents with water
• Solvent-free reactions: Eliminates solvent waste
• Catalytic reactions: Reduces energy requirements and waste
• Microbial transformations: Environmentally friendly alternatives
• Electrochemical reactions: Avoids chemical oxidants/reductants
• Photochemical reactions: Uses light energy instead of reagents

Resources for Further Learning

Chemical Reaction Databases

• NIST Chemical Kinetics Database
• Chemical Reactivity Database (CRD)
• Organic Reactions Database
• Reaxys
• SciFinder

Important Reference Books

• March’s Advanced Organic Chemistry
• Organic Chemistry by Clayden, Greeves, Warren
• Inorganic Chemistry by Shriver & Atkins
• Physical Chemistry by Atkins & de Paula
• Comprehensive Organic Transformations by Larock

This cheatsheet provides a structured reference for chemical reactions across various disciplines. For specific reaction details, always consult appropriate reference texts or databases for the most accurate and up-to-date information.