Exothermic and Endothermic Reactions

Exothermic Reactions

• Definition: Reactions that release heat to the surroundings.
• Characteristics:
  • Products have less chemical energy than reactants.
  • Chemical energy is converted to heat, increasing temperature.
• Examples:
  • Combustion reactions (e.g., burning, which produces heat energy).
  • Neutralization reactions.
  • Displacement reactions.

Endothermic Reactions

• Definition: Reactions that absorb heat from the surroundings.
• Characteristics:
  • Products have more chemical energy than reactants.
  • Heat is absorbed to supply extra energy, decreasing temperature.
• Examples:
  • Thermal decomposition.

Specific Heat Capacity (SHC)

• Definition: Amount of heat needed to raise the temperature of 1 gram of a substance by 1°C.
• Unit: Joules per gram per degree Celsius (J/g°C).

Enthalpy Changes

• Formula: Q = m × c × ΔT
  • Q: Heat energy (Joules)
  • m: Mass (grams)
  • c: Specific heat capacity (J/g°C)
  • ΔT: Temperature change (°C)

Calorimetry Experiment

Purpose

• Measure heat using the reaction to heat another substance.

Experimental Setup

• Use of calorimeter, lid, stirrer, thermometer, and spirit burner.
• Materials:
  • 120 cm³ water.
  • Copper calorimeter.
  • Ethanol in a spirit burner.

Procedure

1. Place 120 cm³ of water in the calorimeter.
2. Reposition lid and stirrer.
3. Allow equipment to equilibrate with room temperature (initial temp: 26°C).
4. Weigh spirit burner (192.34 grams).
5. Light burner, place under water, and stir.
6. Measure temperature increase (final temp: 34°C).
7. Extinguish flame, continue stirring as heat spreads.

Calculations

• Mass of Water: 120 grams (since density = 1 g/cm³).
• Temperature Change: 34°C - 26°C = 8°C.
• SHC of Water: 4.19 J/g°C.
• Using Formula Q = m × c × ΔT:
  • Q = 120 g × 4.19 J/g°C × 8°C = 4012.8 Joules
• Heat Gained by Water: 4.0128 kJ

This experiment demonstrates how the heat is transferred from the combustion of alcohols to water, an application of exothermic reactions.