Lecture Notes: Exothermic and Endothermic Reactions

Definitions

• Exothermic:

  • Releases thermal energy (e.g., boiling water cooling down).
  • Energy at the end increases.
  • Examples: Burning wood, fireworks exploding, and self-heating food.
  • Processes: Freezing water, condensation of steam.

• Endothermic:

  • Absorbs thermal energy from surroundings (e.g., ice melting).
  • Energy at the end decreases.
  • Examples: Photosynthesis, cooking an egg, sour candy.
  • Processes: Melting ice, boiling water, evaporation of water.

Key Concepts

• Reactions vs. Processes
  • Reaction: When substances react to form a new product.
  • Process: No new product is made.

Everyday Examples

• Exothermic:
  • Self-heating cans, hand warmers.
• Endothermic:
  • Ice packs, sherbet sweets.

Reaction Classifications

1. Melting → Endothermic
2. Evaporation → Endothermic
3. Freezing → Exothermic
4. Condensing → Exothermic

Important Chemical Reactions

1. Metal + Oxygen → Metal Oxide
2. Metal + Chlorine → Metal Chloride
3. Metal + Sulfur → Metal Sulfide
4. Metal + Water (liquid) → Metal Hydroxide + Hydrogen
5. Metal + Water (gas) → Metal Oxide + Hydrogen
6. Metal + Acid → Salt + Hydrogen
   • Metal + Hydrochloric Acid → Metal Chloride + Hydrogen
   • Metal + Sulfuric Acid → Metal Sulfate + Hydrogen
   • Metal + Nitric Acid → Metal Nitrate + Hydrogen

Exothermic Reactions

• Burning:

  • Combustion of fuels (e.g., wood, coal) releases heat, light, and sound.
  • Requires fuel, oxygen, and heat.
  • Combustion of hydrogen forms water, releasing energy.

• Reactions with Water and Acid:

  • Potassium's reaction with water forms potassium hydroxide and hydrogen.
  • Magnesium with hydrochloric acid produces heat.

Endothermic Reactions

• Characteristics:
  • Temperature decreases post-reaction.
  • Example: Sherbet sweets dissolve in saliva causing a cool sensation.
  • Stirring potassium chloride in water absorbs heat without forming a new product.

Practical Applications

• Exothermic:
  • Self-heating cans: Calcium oxide and water react to warm the contents.
• Endothermic:
  • Ice packs absorb heat from injuries.

Reactions of Metals

• With Oxygen:

  • Reactive metals like sodium quickly react with oxygen.
  • Inert metals (e.g., gold) do not react.
  • Iron reacts slowly causing rust (Iron + Oxygen → Iron Oxide).

• With Water:

  • Highly reactive metals like sodium react rapidly.
  • Magnesium reacts with steam faster than liquid water.

• With Acid:

  • Reactive metals produce salts and hydrogen gas (e.g., Magnesium + Hydrochloric Acid).
  • Non-reactive metals like gold do not react.

Additional Notes

• Exothermic Reactions:
  • Release energy making surroundings warmer (e.g., fireworks, burning candles).
• Endothermic Reactions:
  • Absorb energy, cooling surroundings (e.g., melting ice, cooking eggs).

Reactive and Unreactive Metals

• Reactive with Oxygen: Sodium, potassium
• Unreactive with Oxygen: Gold
• Reactive with Water: Sodium, potassium
• Unreactive with Water: Copper
• Reactive with Acids: Calcium, magnesium
• Unreactive with Acids: Gold, silver, copper

This summary provides a comprehensive overview of exothermic and endothermic reactions, their properties, examples, and applications, as covered in the lecture.