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Unit 4: Chemical Reactions

9 dot points across 9 inquiry questions. Click any dot point for a focused answer with worked past exam questions where available.

What macroscopic and particulate evidence tells us that a chemical reaction has occurred?

Topic 4.1 Introduction for Reactions: identify the evidence that a chemical reaction has occurred and distinguish chemical changes from physical changes at the macroscopic and particle levels.
A focused answer to AP Chemistry Topic 4.1, covering the macroscopic evidence for a chemical reaction, the distinction between chemical and physical change, and how reactions are seen at the particulate level as rearrangements of atoms, with full worked examples.
9 min answer →

How does the Bronsted-Lowry model describe acids and bases as proton donors and acceptors, and what are conjugate pairs?

Topic 4.8 Introduction to Acid-Base Reactions: apply the Bronsted-Lowry model to identify acids, bases and conjugate acid-base pairs, and write acid-base reactions as proton transfers.
A focused answer to AP Chemistry Topic 4.8, covering the Bronsted-Lowry definitions of acid and base, proton transfer, conjugate acid-base pairs, and the difference between strong and weak acids and bases, with full worked examples.
9 min answer →

How does a titration use a reaction of known stoichiometry to find an unknown concentration?

Topic 4.6 Introduction to Titration: use titration data and reaction stoichiometry to determine the concentration of an unknown solution, distinguishing the equivalence point from the endpoint.
A focused answer to AP Chemistry Topic 4.6, covering the titration method, the equivalence point versus the endpoint, and how to use moles, the reaction mole ratio and volume to calculate an unknown concentration, with full worked examples.
9 min answer →

How do we write a net ionic equation that shows only the species that actually take part in a reaction?

Topic 4.2 Net Ionic Equations: write balanced molecular, complete ionic and net ionic equations for reactions in aqueous solution, removing spectator ions.
A focused answer to AP Chemistry Topic 4.2, covering molecular, complete ionic and net ionic equations, how to identify and cancel spectator ions, and how solubility rules guide which species are written as ions, with full worked examples.
10 min answer →

How do we assign oxidation numbers, identify what is oxidized and reduced, and balance a redox reaction using half-reactions?

Topic 4.9 Oxidation-Reduction (Redox) Reactions: assign oxidation numbers, identify the species oxidized and reduced and the oxidizing and reducing agents, and balance redox reactions using half-reactions.
A focused answer to AP Chemistry Topic 4.9, covering oxidation-number rules, identifying oxidation and reduction, oxidizing and reducing agents, and balancing redox reactions by half-reactions including electron and charge balance, with full worked examples.
10 min answer →

What is the difference between a physical change that affects intermolecular forces and a chemical change that breaks covalent bonds?

Topic 4.4 Physical and Chemical Changes: distinguish physical changes (affecting intermolecular forces) from chemical changes (breaking and forming chemical bonds) and classify processes accordingly.
A focused answer to AP Chemistry Topic 4.4, covering the distinction between physical changes that overcome intermolecular forces and chemical changes that break and form chemical bonds, with the borderline cases of dissolving, and full worked examples.
9 min answer →

How do symbolic equations and particulate diagrams represent the same reaction, and how does conservation of atoms link them?

Topic 4.3 Representations of Reactions: connect symbolic, particulate and macroscopic representations of a reaction, using conservation of atoms to balance and interpret each.
A focused answer to AP Chemistry Topic 4.3, covering the symbolic, particulate and macroscopic levels of representing a reaction, balancing equations by conservation of atoms, and reading and drawing particulate diagrams of reactions, with full worked examples.
9 min answer →

How do the coefficients of a balanced equation let us calculate amounts of reactants and products, including the limiting reactant?

Topic 4.5 Stoichiometry: use mole ratios from a balanced equation to relate amounts of reactants and products, and determine the limiting reactant, theoretical yield and percent yield.
A focused answer to AP Chemistry Topic 4.5, covering mole ratios from balanced equations, mass-to-mass calculations, the limiting reactant, theoretical yield and percent yield, with full worked examples.
10 min answer →

How do we classify a reaction as precipitation, acid-base or oxidation-reduction, and what drives each?

Topic 4.7 Types of Chemical Reactions: classify reactions as precipitation, acid-base, or oxidation-reduction, and identify the driving force of each.
A focused answer to AP Chemistry Topic 4.7, covering the three major reaction types (precipitation, acid-base, oxidation-reduction), the driving force behind each, and how to recognize them from the species and changes involved, with full worked examples.
9 min answer →