AP Chemistry Unit 4 Review: Chemical Reactions

Introduction

• Presenter: Jeremy Krug
• Content: Overview of Unit 4 focusing on Chemical Reactions.
• Resources: Available at Ultimate Review Packet dot com.

Types of Changes

Physical Changes

• Change in appearance or state.
• Examples:
  • Phase Changes: Melting, boiling.
  • Separation of Mixtures: Chromatography, distillation.

Chemical Changes

• Transformation into new substances.
• Indicators of Chemical Change:
  • Light emission.
  • Gas production.
  • Temperature change.
  • Color change.
  • Precipitate formation.

Chemical Equations

• Representation of chemical reactions.
• Balancing Equations: Essential for conserving mass and atoms.
• Net Ionic Equations:
  • Exclude spectator ions.
  • Example: Potassium chloride and silver nitrate forming silver chloride precipitate.

Diagramming Chemical Reactions

• Conservation of Atoms: Important for diagram accuracy.
  • Example: Nitrogen and oxygen in nitrogen monoxide reactions.
• Mole Ratios: Crucial for balancing.

Chemical vs Physical Changes

• Dissolving Ionic Compounds: Sometimes considered a chemical change.
  • Example: Sodium chloride in water.
  • Ion-Dipole Forces: Stronger than crystal lattice.

Calculations with Chemical Equations

• Three-Step Process:
  1. Convert to moles.
  2. Use mole ratios from balanced equation.
  3. Convert to desired final unit (e.g., grams).
• Limiting Reactants: Determine by comparing product amounts from different reactants.
• Molality and Ideal Gas Law: Alternative methods for calculating moles.

Titrations

• Laboratory Experiment: Using a buret to add solution to a flask.
• Acid-Base Titration: Common form.
  • Equivalence Point: Moles of base equal moles of acid.
  • Endpoint: Color change indicating reaction completion.

Types of Chemical Reactions

Acid-Base Reactions

• Proton Transfer: H+ ion.

Oxidation-Reduction Reactions

• Electron Transfer:
  • Oxidation: Loss of electrons.
  • Reduction: Gain of electrons.
  • Determining Oxidation States: Use algebraic methods if not obvious.

Precipitation Reactions

• Formation of Solid Precipitate: Two soluble ionic compounds form an insoluble product.
• Solubility Rules: Alkali metals, ammonium, nitrates always soluble.

Bronsted-Lowry Acid-Base Theory

• Definitions: Acids donate protons, bases accept protons.
• Conjugate Acid-Base Pairs: Acid has one more H+ than its conjugate base.

Strong and Weak Acids/Bases

• Reaction Completion: Strong acids donate all protons; weak bases accept few protons.
• Conjugate Relationship: Stronger the acid, weaker its conjugate base.

Redox Reactions

• Half-Reactions: Visualizing electron transfer.
• Balancing Charges: Required for accurate equation representation.