3.2.1 Internal Energy

• Internal energy

  Total energy contained within a system due to the kinetic and potential energies of its particles
• Kinetic Energy

  • Energy associated with the motion of particles within a substance
  • In gases, particles move rapidly, contributing significantly to internal energy
  • In liquids and solids, movement is less pronounced but still present
• Potential Energy

  • Energy associated with the positions and interactions of particles in a substance
  • In solids, significant due to strong forces holding particles in place
  • In liquids, due to weaker intermolecular forces
  • In gases, minimal due to large distances between particles
• Factors Affecting Internal Energy

  • Temperature
  • State of Matter
  • Mass
• Increasing the temperature of a substance

  Increases the average kinetic energy of its particles, thus increasing the internal energy
• State of Matter

  • Affects the internal energy because it influences the arrangement and movement of particles
  • Solids: Low kinetic energy, high potential energy due to strong intermolecular bonds
  • Liquids: Medium kinetic and potential energy
  • Gases: High kinetic energy, low potential energy due to weak intermolecular forces
• Larger masses

  Have more particles, so they have greater internal energy for the same temperature
• During a Change of State

  1. Melting: Internal energy increases as heat is absorbed

  2. Freezing: Internal energy decreases as heat is released

  3. Boiling/Evaporation: Internal energy increases as heat is absorbed

  4. Condensation: Internal energy decreases as heat is released
• Heat Transfer

  • Transfer of thermal energy between objects or systems due to a temperature difference
  • Conduction: Transfer of heat through direct contact of particles
  • Convection: Transfer of heat through fluid movement
  • Radiation: Transfer of heat through electromagnetic waves
• When heat is added to a system

  The internal energy increases, leading to a rise in temperature or a change in state
• When heat is removed

  The internal energy decreases, leading to a drop in temperature or a change in state
• First Law of Thermodynamics
• ΔU

  Change in internal energy
• Q

  Heat added to the system
• W

  Work done by the system
• Understanding internal energy helps explain various physical processes, from everyday heating and cooling to complex thermodynamic systems