Study Notes
Enthalpy change (ΔH) refers to the heat content change during a chemical reaction, which can be exothermic or endothermic.
- Exothermic Reaction — a reaction that releases energy into the surroundings, increasing the temperature. Example: Combustion, oxidation, and neutralization reactions.
- Endothermic Reaction — a reaction that absorbs energy from the surroundings, decreasing the temperature. Example: Thermal decomposition.
- Activation Energy (Ea) — the minimum energy required to start a chemical reaction. Example: Energy level diagrams show Ea for exothermic and endothermic reactions.
- Bond Energy — the energy required to break a bond or released when a bond is formed. Example: Calculating energy change using bond energies involves subtracting energy out from energy in.
- Standard Conditions — conditions under which thermodynamic measurements are taken, usually 298K and 101 kPa. Example: Used in calculating standard enthalpy changes.
Exam Tips
Key Definitions to Remember
- Enthalpy change (ΔH)
- Exothermic reaction
- Endothermic reaction
- Activation energy (Ea)
- Bond energy
Common Confusions
- Mixing up exothermic and endothermic reactions
- Forgetting to use standard conditions in calculations
Typical Exam Questions
- What is an exothermic reaction? A reaction that releases energy to the surroundings, increasing the temperature.
- How do you calculate the energy change using bond energies? Subtract the total bond energy of products from the total bond energy of reactants.
- What role does a catalyst play in a reaction? It provides an alternative pathway with lower activation energy, increasing the reaction rate.
What Examiners Usually Test
- Understanding of energy level diagrams
- Ability to calculate enthalpy changes using bond energies
- Application of standard conditions in enthalpy calculations