Thermal Physics Fundamentals

Fundamental Concepts

• Thermal physics studies the macroscopic properties of systems with many particles, focusing on heat, work, and temperature relationships.
• The zeroth law of thermodynamics defines thermal equilibrium: if two systems are in equilibrium with a third, they are in equilibrium with each other.
• The first law of thermodynamics states energy conservation: the change in internal energy equals heat added minus work done.
• The second law of thermodynamics states that the total entropy of an isolated system increases over time, or remains constant in ideal cases. This explains the direction of spontaneous processes.
• The third law of thermodynamics states that a perfect crystal's entropy approaches zero as temperature approaches absolute zero.

Temperature and Heat

• Temperature measures the average kinetic energy of particles in a substance. Higher temperature means higher average kinetic energy.
• Heat transfers thermal energy from a hotter object to a colder object due to temperature difference, until equilibrium.
• Specific heat capacity is the heat needed to change a substance's temperature by one degree Celsius (or Kelvin) per unit mass.
• Heat transfer occurs through conduction, convection, and radiation.

Thermodynamic Processes

• Isothermal processes maintain a constant temperature.
• Adiabatic processes have no heat transfer.
• Isobaric processes maintain constant pressure.
• Isochoric processes maintain constant volume.
• Cyclic processes return a system to its initial state through a series of changes.

Ideal Gases

• An ideal gas is a theoretical gas with point particles interacting only through perfectly elastic collisions.
• The ideal gas law relates pressure, volume, temperature, and moles of an ideal gas: PV = nRT. (P = pressure, V = volume, n = moles, R = ideal gas constant, T = temperature)
• The kinetic theory of gases explains macroscopic gas properties through the motion of particles. It links macroscopic quantities (like pressure, temperature) to microscopic properties (like average kinetic energy of molecules).

Entropy

• Entropy measures a system's disorder or randomness.
• Higher entropy means a more disordered state.
• Entropy is crucial in the second law, guiding spontaneous processes towards greater disorder.
• Entropy changes can be calculated for various processes.

Phase Transitions

• Phase transitions change a substance's physical state (e.g., solid to liquid, liquid to gas).
• Phase transitions are associated with enthalpy changes (latent heat).
• Melting, vaporization, and sublimation are examples of phase transitions.
• The Clausius-Clapeyron equation links vapor pressure to temperature during a phase transition.

Applications

• Thermal physics principles are vital in engineering, chemistry, and materials science.
• Thermodynamic concepts help understand heat engines and refrigerators.
• These concepts apply to power generation, refrigeration, and other technologies.
• Thermal physics allows predicting and controlling system behavior under different temperatures and pressures.