Exothermic Reactions Lecture Notes
Introduction to Exothermic Reactions
- Definition: An exothermic reaction is a chemical reaction with a negative overall standard enthalpy change (H).
- Heat Release: These reactions typically release heat.
- Exothermic vs Exergonic:
- Exothermic relates to enthalpy change (H).
- Exergonic relates to Gibbs energy change (G).
- Strongly exothermic reactions are often exergonic.
Examples of Exothermic Reactions
- Thermite Reaction: Reduction of iron(III) oxide by aluminium, producing molten iron.
- Combustion: Burning hydrocarbons, e.g., methane:
- Reaction: CH4 + 2O2 → CO2 + 2H2O
- Enthalpy Change: H = - 890 kJ/mol
- Acid-Base Reactions: Combining strong acids and bases.
- Polymerizations: Exothermic processes in certain polymer reactions.
- Everyday Example: Hand warmers using iron oxidation:
- Reaction: 4Fe + 3O2 → 2Fe2O3
- Enthalpy Change: H = - 1648 kJ/mol
Controlled vs Uncontrolled Reactions
- Uncontrolled Reactions: Lead to fires/explosions, difficult to capture energy.
- Controlled Reactions in Nature:
- Example: Aerobic respiration capturing energy to form ATP, avoiding fires.
Measuring Exothermic Reactions
- Enthalpy (H): Represents the system's energy change.
- Calorimetry: Technique for measuring heat production or absorption.
- Instruments: Bomb calorimeter, reaction calorimeter.
- Standard Enthalpy Change:
- Measured in Joules per mole (formerly cal/mol).
- Calculated using the bond energy differences between reactants and products.
Energy Profile of Exothermic Reactions
- Enthalpy Change (H): Negative value due to higher energy in reactants than products.
- Example: Hydrogen burning:
- Reaction: 2H2 (g) + O2 (g) → 2H2O (g)
- Enthalpy Change: H = 483.6 kJ/mol
Additional Resources
- Related Topics: Chemical thermodynamics, calorimetry, exergonic vs endergonic reactions.
These notes provide a summary of the key concepts related to exothermic reactions, including definitions, examples, measurement techniques, and distinctions from similar reactions.