# Reactivity 3: Equilibrium and Organic Chemistry

> IB Chemistry SL · IB SL Chemistry
> Source: https://www.owlsprep.com/study/ib-chemistry-sl-u6-overview/
> Weight: 15-20% of overall IB Chemistry SL exam

This unit combines two core high-weight IB Chemistry SL topics: fundamental principles of chemical equilibrium, and the foundations of organic reactivity. These concepts form a large portion of your exam and underpin all advanced chemistry studies.

**Prerequisites:** [Stoichiometric relationships](https://www.owlsprep.com/study/ib-chemistry-sl-u1-overview/); [Chemical bonding and structure](https://www.owlsprep.com/study/ib-chemistry-sl-u3-overview/)

## Learning objectives

- Distinguish dynamic equilibrium from static processes and predict shifts in equilibrium position using Le Châtelier's principle
- Name and draw organic compounds correctly following IUPAC nomenclature rules
- Classify common organic functional groups and predict their characteristic reactions
- Describe core organic reaction mechanisms and identify stereoisomerism in simple organic compounds

## 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](https://www.owlsprep.com/study/ib-chemistry-sl-u6-dynamic-equilibrium/) — Introduces the definition and key properties of dynamic equilibrium in closed reversible systems.
- [Position of equilibrium](https://www.owlsprep.com/study/ib-chemistry-sl-u6-position-of-equilibrium/) — Covers Le Châtelier's principle and how conditions alter equilibrium position for reversible reactions.
- [Introduction to organic chemistry](https://www.owlsprep.com/study/ib-chemistry-sl-u6-introduction-to-organic-chemistry/) — Covers IUPAC naming, drawing structures, and classification of simple organic compounds.
- [Functional group chemistry](https://www.owlsprep.com/study/ib-chemistry-sl-u6-functional-group-chemistry/) — Explores typical reactions of all common organic functional groups required for IB SL.
- [Organic reaction mechanisms](https://www.owlsprep.com/study/ib-chemistry-sl-u6-organic-reaction-mechanisms/) — Introduces bond fission and core SL organic mechanism types (free radical, nucleophilic substitution).
- [Introduction to stereochemistry](https://www.owlsprep.com/study/ib-chemistry-sl-u6-introduction-to-stereochemistry/) — Explains structural vs stereoisomerism, including cis-trans and optical isomerism for SL.

## Common pitfalls

- **Wrong:** Confusing dynamic equilibrium with equal concentrations of reactants and products
  - Why it fails: Equilibrium is defined by equal reaction rates, not equal concentrations
  - Correct: Remember: at equilibrium, forward and reverse rates are equal, and concentrations are constant (not equal)
- **Wrong:** Ignoring mole counts of gas when applying Le Châtelier's principle to pressure changes
  - Why it fails: Pressure changes only shift equilibrium if total moles of gas differ between reactants and products
  - Correct: Count moles of gas on both sides of the equation before predicting an equilibrium shift
- **Wrong:** Numbering the carbon chain from the wrong end for IUPAC naming
  - Why it fails: Functional groups get higher priority than alkyl branches when numbering the parent chain
  - Correct: Always number the parent chain to give the highest priority functional group the lowest possible number

## 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.

- [Dynamic equilibrium](https://www.owlsprep.com/study/ib-chemistry-sl-u6-dynamic-equilibrium/)
- [Position of equilibrium](https://www.owlsprep.com/study/ib-chemistry-sl-u6-position-of-equilibrium/)
- [Introduction to organic chemistry](https://www.owlsprep.com/study/ib-chemistry-sl-u6-introduction-to-organic-chemistry/)

---

From [OwlsPrep](https://www.owlsprep.com) — free study guides for A-Level, IB, AP and IGCSE, written against the official syllabus. Canonical page: https://www.owlsprep.com/study/ib-chemistry-sl-u6-overview/