Unit Overview
R2: How much / how fast / how far?
IB Chemistry HLΒ· 6 min read π n/a
1. Unit at a Glance
This unit follows the natural order chemists use to analyze any reaction: first we calculate how much reactant is consumed and how much product is formed (stoichiometry), then we examine how fast the reaction proceeds (kinetics), and finally we determine how far the reaction will go before reaching a steady state (equilibrium).
Core standard level (SL) content is covered first for each theme, followed by additional higher level (AHL) extensions that deepen conceptual understanding and problem-solving skills for exam success.
Below are all sub-topics in this unit:
Stoichiometric relationships
Introduces the mole concept and calculates mass, mole, and gas volume relationships
β β β± 10 min
Limiting and excess reactants
Identifies limiting reactants and calculates percent yield for chemical reactions
β β β± 8 min
Reaction rate and rate expressions
Defines reaction rate and explains how to measure rate experimentally
β β β± 7 min
Collision theory
Explains how temperature, concentration and catalysts affect reaction rate
β β β± 7 min
Dynamic equilibrium
Describes reversible reactions and the nature of dynamic equilibrium
β β β β± 6 min
The equilibrium constant
Writes equilibrium constant expressions for homogeneous reaction systems
β β β β± 8 min
Solubility equilibria
Applies equilibrium principles to sparingly soluble ionic compounds
β β β β± 8 min
AHL: Advanced stoichiometry and titration calculations
Solves complex titration problems including back titration calculations
β β β β β± 12 min
AHL: Rate laws and reaction order
Calculates reaction order, rate constants, and half-lives from experimental data
β β β β β± 12 min
AHL: Activation energy and Arrhenius equation
Uses the Arrhenius equation to relate temperature to rate constant
β β β β β± 10 min
AHL: Extended Le Chatelier's principle
Predicts how changing conditions affect equilibrium position and
β β β β± 8 min
AHL: Reaction quotient
Uses reaction quotient to predict the direction of a reaction shift
β β β β± 7 min
2. Common Pitfalls
Wrong move:
Confusing reaction rate with reaction order in kinetics
Why:
Rate changes with reactant concentration but reaction order is a constant for a given reaction
Correct move:
Remember rate is the change in concentration over time, while order is the exponent in the rate law expression
Wrong move:
Forgetting to apply balanced equation coefficients to mole ratios in stoichiometry
Why:
Skipping this step leads to incorrect limiting reactant and yield calculations
Correct move:
Always write the mole ratio explicitly from the balanced equation before solving problems
Wrong move:
Confusing the reaction quotient with the equilibrium constant
Why:
Both use the same expression format but rely on different concentration values
Correct move:
uses only equilibrium concentrations, while uses concentrations at any non-equilibrium point
3. Quick Reference Cheatsheet
Concept / Formula | Key Use Case |
|---|---|
Calculate moles from mass and molar mass | |
Percent Yield = | Calculate reaction efficiency |
Average Rate = | Calculate average reaction rate from experimental data |
for | Write equilibrium constant expressions |
Rate Law: | Relate reactant concentration to reaction rate |
Arrhenius Equation: | Relate activation energy to rate constant and temperature |
Predict direction of reaction shift when | |
Calculate solubility product for sparingly soluble salts |
What's Next
Start with the first sub-topic of this unit to build your foundational understanding of stoichiometry, the first core theme of this unit. Work through each sub-topic in order, as concepts build sequentially throughout the unit. Once you complete all sub-topics in this unit, you will move on to the next unit covering acids and bases.