Zeroth Law of Thermodynamics

Introduction

• Energy studied previously includes mechanical and thermal forms.
• Mechanical energy applies to tangible objects through potential and kinetic energy.
• Potential energy turns into kinetic energy as it loses potential energy.
• Total mechanical energy (E) equals the sum of kinetic and potential energies.
• Changes of the system's total mechanical energy (ΔE) are important from a physics perspective.
• Thermal energy comes from rapid, random motion of molecules, atoms, and subatomic particles.
• Thermal energy can be split into potential and kinetic energy.
• Particle motion creates kinetic energy and average kinetic energy relates to temperature.

The Zeroth Law of Thermodynamics

• The zeroth law states that systems in thermal equilibrium must be in thermal equilibrium with each other.
• If no net energy exchange occurs between systems A and B, then none will occur when they can exchange thermal energy directly.
• When systems A and B are at the same temperature as C, they are at the same temperature as each other.
• If all systems are at the same temperature there is no thermal energy flow.

The General Law of Conservation of Energy - The First Law

• Energy can be added to a system through work (Wnet) via external nonconservative forces or heat transfer (Q) via temperature differences.
• Transferred energy changes the system's internal energy (ΔU), mechanical energy (ΔE), or both.
• The general energy conservation law is Q + Wnet = ΔU + ΔE.
• Ideal insulating walls that do not allow for thermal energy to pass are adiabatic boundaries.
• Ideal conductors of thermal energy are diathermic materials, though completely adiabatic or diathermic materials do not exist.
• Equation 16.3 is the mathematical form of the first law of thermodynamics that extends the principle of mechanical energy conservation to internal energy.

Heat Engines

• Heat engines perform mechanical work by absorbing & discharging heat.
• An expanding gas in an expandable container converts thermal energy to work.
• To solve uneven heating/cooling of expanding gasses it involves incremental expansion allowing thermal equilibrium, called a quasi-static process.
• For quasi-static processes, internal gas pressure is in equilibrium with external pressure.
• Equation 16.4 is the simplified formula for work is W = Fd.

Internal Energy

• A substance's particles possess potential energies that are extremely difficult to determine with reference points.
• Internal energy (U) represents the sum total of particle kinetic and potential energies.
• Changes in internal energy (ΔU) of a system are more important and easier to calculate than internal energy states.

Entropy

• Entropy (S) increases in all natural processes.
• Entropy is another state variable of a system related to microscopic properties.
• As with internal energy, the change of entropy (ΔS) is more important than entropy.
• One form of the second law of thermodynamics is the principle that energy flows from high to low concentration. Entropy is defined as ΔS = ΔQ/T.

Isolated System Constant Energy

• In an isolated system, energy is conserved where it may shift from one form to the next, but does not appear, leave or disappear.
• The universe as an isolated system adheres to that standard with all the energy constantly being the equivalent.

Types of Thermodynamic Systems

• An open system (e.g. ice cube) exchanges energy/matter with surroundings.
• A closed system (e.g. gas in conducting cylinder) exchanges energy (not matter) with surroundings.
• An isolated system (e.g. liquid in vacuum flask) exchanges neither energy nor matter with surroundings.
• The Universe is the only truly isolated system.

Introduction to mechanical and thermal energy. Discussion of the Zeroth Law of Thermodynamics, which states that systems in thermal equilibrium must be in thermal equilibrium with each other. Includes total mechanical energy and system changes.