Unit Overview
Reactivity 3: Equilibrium and Organic Chemistry
IB Chemistry SL· 6 min read 📊 15-20% of overall IB Chemistry SL exam
1. Unit at a Glance
This unit is split into two connected thematic halves. We begin with chemical equilibrium, exploring the reversible nature of many reactions, how external conditions alter equilibrium position, and core underlying rules. We then move to organic chemistry, the study of carbon-based compounds that form the basis of biochemistry, pharmaceuticals, and modern materials.
We build from foundational concepts up to applied skills: you will start by learning what equilibrium is, then learn to predict shifts, then move to naming organic compounds, before exploring functional group reactivity, reaction mechanisms, and stereoisomerism. Sub-topics build sequentially, so we recommend working through them in order.
Ordered sub-topics for this unit:
Dynamic equilibrium
Introduces the definition and key properties of dynamic equilibrium in closed reversible systems.
★★⏱ 7 min
Position of equilibrium
Covers Le Châtelier's principle and how conditions alter equilibrium position for reversible reactions.
★★★⏱ 8 min
Introduction to organic chemistry
Covers IUPAC naming, drawing structures, and classification of simple organic compounds.
★★⏱ 10 min
Functional group chemistry
Explores typical reactions of all common organic functional groups required for IB SL.
★★★⏱ 12 min
Organic reaction mechanisms
Introduces bond fission and core SL organic mechanism types (free radical, nucleophilic substitution).
★★★★⏱ 10 min
Introduction to stereochemistry
Explains structural vs stereoisomerism, including cis-trans and optical isomerism for SL.
★★★★⏱ 8 min
2. Common Pitfalls
Wrong move:
Confusing dynamic equilibrium with equal concentrations of reactants and products
Why:
Equilibrium is defined by equal reaction rates, not equal concentrations
Correct move:
Remember: at equilibrium, forward and reverse rates are equal, and concentrations are constant (not equal)
Wrong move:
Ignoring mole counts of gas when applying Le Châtelier's principle to pressure changes
Why:
Pressure changes only shift equilibrium if total moles of gas differ between reactants and products
Correct move:
Count moles of gas on both sides of the equation before predicting an equilibrium shift
Wrong move:
Numbering the carbon chain from the wrong end for IUPAC naming
Why:
Functional groups get higher priority than alkyl branches when numbering the parent chain
Correct move:
Always number the parent chain to give the highest priority functional group the lowest possible number
3. Quick Reference Cheatsheet
Key Concept | Core Rule/Formula |
|---|---|
Dynamic equilibrium | Rate of forward reaction = Rate of reverse reaction; concentrations are constant |
Le Châtelier's Principle | A system at equilibrium shifts to counteract any externally imposed change |
IUPAC Naming Priority | Carboxylic acids > alcohols > alkenes > alkanes for parent chain numbering |
Free Radical Substitution | Three distinct stages: Initiation → Propagation → Termination |
Nucleophilic Substitution | Electron-rich nucleophile attacks an electron-deficient carbon center |
Stereoisomerism | Same molecular and structural formula, different spatial arrangement of atoms |
What's Next
Begin this unit with the first sub-topic on dynamic equilibrium, which forms the foundation for all equilibrium concepts covered later in the unit. Once you complete all sub-topics in this unit, move on to the first sub-topic of the next unit covering measurement and data processing for IB Chemistry SL.