AP Chemistry Unit 4: Chemical Reactions Review

Introduction

• Presenter: Jeremy Krug
• Provides a 10-minute review of AP Chemistry Unit 4
• Additional resources available at Ultimate Review Packet dot com

Types of Changes

Physical Changes

• Changes in appearance or state
• Examples: phase changes (melting, boiling), separating mixtures (chromatography, distillation)

Chemical Changes

• Transformation into new substances
• Involves breaking and forming chemical bonds
• Indicators: light emission, gas production, temperature change, color change, precipitate formation

Chemical Equations

• Used to represent reactions
• Must be balanced to conserve mass and atoms
• Net Ionic Equations:
  • Example with potassium chloride and silver nitrate
  • Omit spectator ions to focus on the reaction

Diagramming Chemical Reactions

• Conserve all atoms in diagrams
• Example: Balancing reactants and products in reaction diagrams
• Respect mole ratios

Chemical Bonds and Dissolution

• Dissolving ionic compounds in water can be seen as a chemical change
• Example: Sodium chloride dissolving – breaking ionic bonds, forming ion-dipole forces with water

Stoichiometry

• Three-Step Process for calculating product mass:
  1. Convert to moles
  2. Use mole ratio from balanced equation
  3. Convert to final unit (grams)
• Limiting reactant problems and molarity as conversion factor

Titrations

• Laboratory method using a buret to add solution until reaction occurs
• Acid-Base Titration:
  • Base in buret, acid in flask
  • Equivalence point: moles of base = moles of acid
  • Endpoint: indicator changes color

Types of Chemical Reactions

Acid-Base Reactions

• Transfer of a proton (H+ ion)
• Bronsted-Lowry definitions: acid is proton donor, base is proton acceptor

Oxidation-Reduction Reactions (Redox)

• Transfer of electrons
• Oxidation: species loses electrons
• Reduction: species gains electrons
• Determine oxidation states and balance half-reactions

Precipitation Reactions

• Formation of a solid precipitate from soluble ionic compounds
• Solubility rules: alkali metals, ammonium, nitrates always soluble

Conjugate Acid-Base Pairs

• Acid has one more H+ than its conjugate base
• Water can act as acid or base
• Strong acids donate most protons, weak conjugate bases

Redox Reactions

• Written as half-reactions to show electron transfer
• Balance charges with electrons
• Example: Zinc and gold ions exchanging electrons

Conclusion

• Encouragement to continue learning chemistry
• Next review topic: Unit 5 on Kinetics