Lecture Notes: Thermal Energy, Temperature, and Heat

Definitions

• Thermal Energy:

  • Type of kinetic energy due to the motion of atoms or molecules
  • Associated with how fast atoms or molecules are moving

• Temperature:

  • Quantitative measure of how hot or cold something is
  • Higher temperature indicates faster movement of atoms (e.g., in a hot liquid)
  • Lower temperature indicates slower movement of atoms (e.g., in a cold liquid)

Heat (Q)

• Transfer of thermal energy
• Occurs when energy moves from a hotter object to a colder one
• Affects solids, liquids, and gases

Heat in Chemistry

• Focus on chemical reactions and how they produce heat

Types of Reactions

1. Exothermic Reactions:

   • Release heat
   • Reaction: A → B + Heat
   • Feels hot due to heat release
   • Example: Combustion reactions
     • Burning, such as acetylene with oxygen
     • Used in welding and cutting metals

2. Endothermic Reactions:

   • Absorb heat
   • Reaction requires input of heat
   • Feels cold as it absorbs heat from surroundings
   • Example: Use of ice packs
     • Ammonium nitrate dissolving in water
     • Absorbs heat causing it to feel cold

Key Concepts

• Heat Transfer: Involves energy moving from a warmer to a cooler object
• Movement of Atoms: Faster in hot substances, slower in cold
• Exothermic vs. Endothermic:
  • Exothermic: Heat is a product and feels hot
  • Endothermic: Heat is absorbed, feels cold