Summary Grade 12 Chemistry – Unit 2: Energy Changes & Rates of Reaction

Grade 12 Chemistry – Unit 2: Energy Changes &
Rates of Reaction
Comprehensive Notes (Clean • Organized • Student-Friendly)




Table of Contents
1. Introduction to Energy in Chemical Systems
2. Types of Energy & Energy Transformations
3. Thermochemistry Basics
4. Enthalpy (ΔH) & Potential Energy Diagrams
5. Calorimetry
6. Hess’s Law & Enthalpy Calculations
7. Rates of Reaction: Theory & Factors
8. Collision Theory
9. Rate Laws & Reaction Mechanisms
10. Catalysts & Activation Energy
11. Practice Problems




1. Introduction to Energy in Chemical Systems
Chemical reactions involve energy transformations. Bonds breaking and forming release or absorb
energy, influencing the reaction’s speed and feasibility.


Energy changes allow us to understand:


• Why some reactions occur spontaneously
• Why some reactions require heat
• How much energy is absorbed or released




2. Types of Energy & Energy Transformations
2.1 Kinetic Energy (Ek)
Energy of motion. Higher temperature = higher kinetic energy.




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, 2.2 Potential Energy (Ep)
Stored energy, often in chemical bonds.


2.3 Chemical Energy
Energy stored in bonds between atoms.


2.4 Thermal Energy
Energy associated with temperature.


Energy Transformations Example:

Chemical Potential Energy → Thermal Energy + Kinetic Energy


Example: combustion of methane.




3. Thermochemistry Basics
Thermochemistry studies heat changes during chemical reactions.


3.1 System vs. Surroundings
• System: chemicals reacting
• Surroundings: everything else


3.2 Exothermic Processes
• Release heat to surroundings
• Surroundings warm up

Example: combustion


Equation format:



reactants → products + energy




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