AP Chemistry Lecture: Unit 4 - Chemical Reactions

Introduction

• Lecturer: Mr. Lambert
• Lecture focuses on Unit 4: Chemical Reactions in AP Chemistry.
• Reference materials:
  • Bookwork Problems: Available in Google Classroom.
  • Outline Chapters: Check Google Classroom.

Chemical Changes

Physical vs. Chemical Changes

• Physical Changes:

  • Substance changes properties but remains the same.
  • No change in composition.
  • Examples include phase changes, mixtures forming/separating, cutting, and color changes (e.g., painting).

• Chemical Changes:

  • New substance is produced.
  • Indicators:
    • Change in energy (endothermic/exothermic).
    • Formation of gas (indicated by bubbles/vapors).
    • Formation of precipitate (solid forms from solution).
    • Color change.
  • Indicators are evidence, not proof, of chemical change.

Ionic Equations and Electrolytes

Electrolytes

• Definition: Substance whose aqueous solutions contain ions.
  • Example: Sodium chloride.
• Types:
  • Strong Electrolytes: Completely dissociate into ions.
  • Weak Electrolytes: Partially dissociate into ions.
  • Non-electrolytes: Stay in molecular form, do not conduct electricity.

Dissociation vs. Ionization

• Ionic Compounds:
  • Dissociate into ions (e.g., NaCl).
• Molecular Compounds:
  • Ionize in solution (e.g., acids like HF).

Types of Electrolytes

• Strong Electrolytes: Salts, strong acids, and strong bases.
• Weak Electrolytes: Weak acids and bases.
• Non-Electrolytes: Organic substances (e.g., sugars, alcohols).

Particle Diagrams

• Strong Electrolyte (e.g., NaCl):
  • Completely dissociated ions are shown.
• Weak Electrolyte (e.g., HF):
  • Both molecules and ions are present.
• Non-Electrolyte (e.g., CO2):
  • Only molecular form is present.

Conductivity of Electrolytes

• Strong Electrolytes: Bright bulb (many ions).
• Weak Electrolytes: Dim bulb (fewer ions).
• Non-Electrolytes: No light (no ions).
• Demonstration Setup:
  • Uses metal plates in water to complete an electrical circuit.