Study Guide Unit 4 AP chemistry

AP Chemistry Unit 4: Chemical Reactions

Topics:

• 4.1 Introduction for Reactions
• 4.2 Net Ionic Equations
• 4.3 Representations of Reactions
• 4.4 Physical and Chemical Changes
• 4.5 Stoichiometry
• 4.6 Introduction to Titration
• 4.7 Types of Chemical Reactions
• 4.8 Introduction to Acid-Base Reactions
• 4.9 Oxidation-Reduction (Redox) Reactions

4.1 Introduction for Reactions

Chemical vs Physical changes explained through examples such as rusting, melting, boiling, and electrolysis. Chemical changes involve bond breaking/forming and result in composition change, whereas physical changes do not alter the chemical identity.

Example: Fe(s) + O2(g) → Fe2O3(s) - Chemical Change
H2O(s) → H2O(l) - Physical Change

4.2 Net Ionic Equations

Focuses on how to write complete ionic and net ionic equations. Explains dissociation in aqueous solutions and how to identify and eliminate spectator ions.

Example: 2KI(aq) + Pb(NO3)2(aq) → PbI2(s) + 2KNO3(aq)
Net Ionic: Pb2+(aq) + 2I-(aq) → PbI2(s)

4.3 Representations of Reactions

Students learn to interpret and draw particulate diagrams that respect conservation of mass and atom count. These diagrams help visualize limiting reagents and excess species.

Includes examples of CH₄ + O₂ combustion and NH₃ synthesis from H₂ and N₂.

4.4 Physical and Chemical Changes

Expands on how to classify changes with deeper context. Dissolving, melting, combustion, and decomposition are discussed with energy considerations.

Example: Electrolysis of water: 2 H2O(l) → 2 H2(g) + O2(g) - Chemical Change

4.5 Stoichiometry

Introduces mole ratios from balanced equations to calculate quantities of substances in reactions. Concepts of limiting reactant and excess reactant are central.

Example: 3 H₂ + N₂ → 2 NH₃
Given 6 mol H₂ and 3 mol N₂ → H₂ limits the reaction.

4.6 Introduction to Titration

Outlines volumetric analysis using a titrant and analyte. Equivalence point, pH indicators, and stoichiometric relationships are introduced.

Example: HCl + NaOH → NaCl + H₂O
Moles NaOH used = M × V → calculate moles HCl → calculate concentration

4.7 Types of Chemical Reactions

• Synthesis: A + B → AB
• Decomposition: AB → A + B
• Single Replacement: A + BC → AC + B
• Double Replacement: AB + CD → AD + CB
• Combustion: Hydrocarbon + O₂ → CO₂ + H₂O

4.8 Introduction to Acid-Base Reactions

Defines acids and bases per Brønsted-Lowry theory. Describes neutralization reactions and introduces conjugate acid-base pairs.

Example: NH₃ + H₂O ⇌ NH₄⁺ + OH⁻
NH₃ is base; H₂O is acid.

4.9 Oxidation-Reduction (Redox) Reactions

Defines oxidation (loss of e⁻) and reduction (gain of e⁻). Covers assigning oxidation numbers and balancing redox equations using half-reactions.

Example: Zn + Cu²⁺ → Zn²⁺ + Cu
Zn is oxidized, Cu²⁺ is reduced.

End of Unit 4 Overview