Thermodynamics Lecture Notes

Introduction to Thermodynamics

• Definition: Study of heat flow (thermo = heat, dynamics = motion of heat)
• Developed in the 1800s during the Industrial Revolution.
• Associated with the use of fossil fuels and the beginning of climate change awareness (first calculations on CO2 impact by Arrhenius).

Historical Context

• Arrhenius (late 1800s) calculated the impact of CO2 on climate, predicting trouble for humanity in 2000 years due to emissions.
• Exponential growth in CO2 since then has accelerated the timeline for climate issues.

Universal Application of Thermodynamics

• Thermodynamics applies to various systems:
  • Biological (energy from food)
  • Mechanical (cars, boats)
  • Astrophysical (stars, black holes)
  • Economic systems (non-equilibrium thermodynamics)
• Initially, it was based on macroscopic properties, now also incorporates microscopic (atomic/molecular) properties.

Laws of Thermodynamics

1. Zeroth Law: Defines temperature.
   • Common-sense law: Heat flows from hot to cold.
2. First Law: Defines energy conservation (U).
   • "You can break even" law: Energy cannot be created or destroyed; it can only be transformed.
3. Second Law: Defines entropy.
   • Direction of time; entropy increases over time.
   • "You can break even at absolute zero" law: Perfect efficiency possible only at 0 K.
4. Third Law: Numerical value of entropy.
   • "You can't get to zero degrees" law: Absolute zero is unattainable.

Importance of Definitions

• Understanding definitions is crucial for solving thermodynamic problems:
  • System: Part of the universe being studied.
  • Surroundings: Everything outside the system.
  • Boundary: Division between system and surroundings (can be real or imaginary).

Types of Systems

• Open System: Mass and energy can flow across the boundary.
• Closed System: Energy can flow, but mass cannot.
• Isolated System: Neither mass nor energy can flow.

Describing the System

• Essential macroscopic properties:
  • Pressure, temperature, volume, number of moles, mass.
• Homogeneous vs Heterogeneous systems:
  • Homogeneous: Uniform composition (e.g., milk coffee).
  • Heterogeneous: Different phases (e.g., ice water).
• Equilibrium systems: Properties do not change over time or space.
• State Variables: Describe equilibrium states (independent of how the state was reached).

Properties of Systems

• Extensive Properties: Depend on the size of the system (e.g., mass, volume).
• Intensive Properties: Independent of system size (e.g., temperature).
• Can derive intensive properties from extensive ones (e.g., molar volume).

Transition Between States

• Describes how to go from one equilibrium state to another using paths.
  • Reversible Path: System remains in equilibrium throughout the process.
  • Irreversible Path: System does not remain in equilibrium; requires energy to return to initial state.

Path Definition and Importance

• Paths can be described using terms such as:
  • Adiabatic: No heat transfer.
  • Isobaric: Constant pressure.
  • Isothermal: Constant temperature.

Zeroth Law of Thermodynamics

• Definition: If two systems are in thermal equilibrium with a third system, then they are in thermal equilibrium with each other.
• Basis for defining temperature and thermometers.

Thermometer Basics

• Must have a substance that changes properties based on temperature (e.g., volume, resistivity).
• Need reference points for temperature scales (e.g., freezing and boiling points of water).
• Overview of historical temperature scales (Celsius, Fahrenheit).

Conclusion

• Next session will cover the ideal gas thermometer and the Kelvin scale.