1.1 Temperature and Thermal Equilibrium

Temperature and thermal equilibrium are key concepts in thermodynamics. They help us understand how heat moves between objects and why things reach the same temperature when left in contact for a while.

These ideas explain everyday experiences, like why your hot coffee cools down or how a fever thermometer works. They also form the basis for more complex thermal systems and energy transfer processes in physics and engineering.

Temperature and Thermal Equilibrium

Temperature in everyday life and science

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• Measures the average kinetic energy of particles in a system
  • Higher temperature means higher average kinetic energy (hot coffee)
  • Lower temperature means lower average kinetic energy (iced tea)
• Everyday examples demonstrate temperature differences
  • A person with a fever has higher body temperature than a healthy person
  • A hot stove burner has higher temperature than a room-temperature countertop
• Scientific concepts define temperature scales and limits
  • Absolute zero is the lowest possible temperature with minimal particle kinetic energy
  • Kelvin scale is an absolute temperature scale with 0 K at absolute zero
  • Celsius and Fahrenheit scales are relative based on specific reference points (freezing and boiling points of water)

Process of thermal equilibrium

• Occurs when two or more systems in thermal contact reach the same temperature
  • No net heat transfer between systems in thermal equilibrium
• Heat always flows from higher-temperature to lower-temperature objects
  • Continues until both objects reach the same temperature and achieve thermal equilibrium
• Rate of heat transfer depends on several factors
  • Temperature difference between the objects
  • Surface area of contact
  • Material properties like thermal conductivity
• Examples demonstrate thermal equilibrium in action
  • A hot metal spoon in cold water eventually reaches water temperature
  • A room-temperature object in a refrigerator cools down to match interior temperature
• Thermal expansion occurs as objects reach thermal equilibrium, affecting their size and shape

Zeroth law for temperature predictions

• States that if two systems are in thermal equilibrium with a third system, they are also in thermal equilibrium with each other
  • If A and C are in thermal equilibrium, and B and C are in thermal equilibrium, then A and B are in thermal equilibrium
• Allows for the concept of temperature and the use of thermometers
  • A thermometer reaches thermal equilibrium with the system it measures
• Predicts temperature changes in interacting systems
  • Heat flows from higher-temperature to lower-temperature objects in thermal contact
  • Final system temperature will be between the initial temperatures of the two objects
  • Specific final temperature depends on heat capacities and masses of the objects
• Applies the zeroth law to real-world situations
  • A room-temperature thermometer in a hot liquid initially reads lower than the liquid but eventually reaches thermal equilibrium and displays liquid temperature
  • Mixing hot and cold water results in a final mixture temperature between the initial temperatures, depending on their relative volumes and temperatures

Heat and Energy in Thermal Systems

• Thermal energy represents the total kinetic energy of particles in a system
• Specific heat capacity determines how much thermal energy a material can store per unit mass and temperature change
• Latent heat is the energy absorbed or released during phase changes without temperature change
• Thermodynamic equilibrium occurs when a system is in thermal, mechanical, and chemical equilibrium simultaneously