Summary Internal Energy, Temperature and Heat

Internal Energy, Temperature and Heat

• Session Goals: Understand definitions and relationships between internal energy, temperature, and heat.

Kinetic Energy of Molecules

• Molecules in substances are in constant motion.

• Forms of Movement:

  • Rotational

  • Vibrational

  • Collisional (energy transfer through translation)

• Translational movement transfers energy between locations.

Temperature

• Temperature is perceived warmth from kinetic energy of molecules.

• Calibrated temperature scales (Celsius, Fahrenheit) relate to observable phenomena (e.g., freezing and boiling points of water).

Kelvin Scale and Absolute Zero

• Lower kinetic energy reflects lower warmth (temperature).

• Absolute Zero:

  • Lowest energy state (0° K / -273° C).

• Kelvin scale has 100 increments between freezing and boiling points like Celsius, but its zero is absolute zero.

Internal Energy

• Internal energy = sum of all kinetic and potential energy in an object (often referred to as thermal energy).

• Changes in internal energy occur through energy transfer or phase changes.

• Phase changes involve potential energy; otherwise, changes relate to molecular kinetic energy.

Temperature vs Internal Energy

• Key Distinction: Temperature does NOT measure total internal energy; it measures translational kinetic energy only.

Heat

• Heat is energy transferred from a warmer object to a cooler object across a temperature gradient (ΔT).

• Heat results in a change in internal energy of objects.

Measurement of Heat

• SI unit of energy = Joule, applicable to heat (energy in transit).

• Other units like calorie and kilocalorie may also be used.

Summary

• Key concepts: definition of internal energy, temperature, heat, and their interrelations.